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mysql-server/sql/sql_select.cc
Ho Sy Tan 4a107fd10e 2025-03-05 14:31:08
2025-03-05 14:31:37 +07:00

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/* Copyright (c) 2000, 2024, Oracle and/or its affiliates.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License, version 2.0,
as published by the Free Software Foundation.
This program is designed to work with certain software (including
but not limited to OpenSSL) that is licensed under separate terms,
as designated in a particular file or component or in included license
documentation. The authors of MySQL hereby grant you an additional
permission to link the program and your derivative works with the
separately licensed software that they have either included with
the program or referenced in the documentation.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License, version 2.0, for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA */
/**
@file sql/sql_select.cc
@brief Evaluate query expressions, throughout resolving, optimization and
execution.
@defgroup Query_Optimizer Query Optimizer
@{
*/
#include "sql/sql_select.h"
#include <stdio.h>
#include <string.h>
#include <algorithm>
#include <atomic>
#include <cstdio>
#include <cstring>
#include <initializer_list>
#include <memory>
#include <string>
#include <string_view>
#include "field_types.h"
#include "lex_string.h"
#include "m_string.h" // native_strncasecmp(), native_strcasecmp()
#include "mem_root_deque.h" // mem_root_deque
#include "my_alloc.h"
#include "my_bitmap.h"
#include "my_byteorder.h" // int8store, uint8korr
#include "my_compiler.h"
#include "my_dbug.h"
#include "my_pointer_arithmetic.h"
#include "my_sqlcommand.h"
#include "my_sys.h"
#include "mysql/plugin.h"
#include "mysql/strings/m_ctype.h"
#include "mysql/udf_registration_types.h"
#include "mysql_com.h"
#include "mysqld_error.h"
#include "scope_guard.h"
#include "sql-common/json_dom.h"
#include "sql-common/my_decimal.h"
#include "sql/auth/auth_acls.h"
#include "sql/auth/auth_common.h" // *_ACL
#include "sql/auth/sql_security_ctx.h"
#include "sql/current_thd.h"
#include "sql/debug_sync.h" // DEBUG_SYNC
#include "sql/enum_query_type.h"
#include "sql/error_handler.h" // Ignore_error_handler
#include "sql/field.h"
#include "sql/filesort.h" // filesort_free_buffers
#include "sql/handler.h"
#include "sql/intrusive_list_iterator.h"
#include "sql/item.h"
#include "sql/item_func.h"
#include "sql/item_json_func.h"
#include "sql/item_subselect.h"
#include "sql/item_sum.h" // Item_sum
#include "sql/iterators/row_iterator.h"
#include "sql/iterators/sorting_iterator.h"
#include "sql/join_optimizer/access_path.h"
#include "sql/join_optimizer/bit_utils.h"
#include "sql/join_optimizer/join_optimizer.h"
#include "sql/join_optimizer/replace_item.h"
#include "sql/key.h" // key_copy, key_cmp, key_cmp_if_same
#include "sql/key_spec.h"
#include "sql/lock.h" // mysql_unlock_some_tables,
#include "sql/mysqld.h" // stage_init
#include "sql/nested_join.h"
#include "sql/opt_explain.h"
#include "sql/opt_explain_format.h"
#include "sql/opt_hints.h" // hint_key_state()
#include "sql/opt_trace.h"
#include "sql/opt_trace_context.h"
#include "sql/parse_tree_node_base.h"
#include "sql/query_options.h"
#include "sql/query_result.h"
#include "sql/range_optimizer/path_helpers.h"
#include "sql/range_optimizer/range_optimizer.h"
#include "sql/set_var.h"
#include "sql/sql_base.h"
#include "sql/sql_class.h"
#include "sql/sql_cmd.h"
#include "sql/sql_do.h"
#include "sql/sql_error.h"
#include "sql/sql_executor.h"
#include "sql/sql_insert.h" // Sql_cmd_insert_base
#include "sql/sql_join_buffer.h" // JOIN_CACHE
#include "sql/sql_lex.h"
#include "sql/sql_list.h"
#include "sql/sql_optimizer.h" // JOIN
#include "sql/sql_parse.h" // bind_fields
#include "sql/sql_planner.h" // calculate_condition_filter
#include "sql/sql_plugin.h"
#include "sql/sql_resolver.h"
#include "sql/sql_test.h" // misc. debug printing utilities
#include "sql/sql_timer.h" // thd_timer_set
#include "sql/sql_tmp_table.h" // tmp tables
#include "sql/system_variables.h"
#include "sql/table.h"
#include "sql/temp_table_param.h"
#include "sql/thd_raii.h"
#include "sql/window.h" // ignore_gaf_const_opt
#include "sql_string.h"
#include "template_utils.h"
#include "thr_lock.h"
using std::max;
using std::min;
using namespace std::literals;
static store_key *get_store_key(THD *thd, Item *val, table_map used_tables,
table_map const_tables,
const KEY_PART_INFO *key_part, uchar *key_buff,
uint maybe_null);
static bool retry_with_secondary_engine(THD *thd);
using Global_tables_iterator =
IntrusiveListIterator<Table_ref, &Table_ref::next_global>;
/// A list interface over the Table_ref::next_global pointer.
using Global_tables_list = IteratorContainer<Global_tables_iterator>;
/**
Check whether the statement is a SHOW command using INFORMATION_SCHEMA system
views.
@param thd Thread (session) context.
@returns true if command uses INFORMATION_SCHEMA system view, false otherwise
*/
inline bool is_show_cmd_using_system_view(THD *thd) {
return sql_command_flags[thd->lex->sql_command] & CF_SHOW_USES_SYSTEM_VIEW;
}
/**
Get the maximum execution time for a statement.
@return Length of time in milliseconds.
@remark A zero timeout means that no timeout should be
applied to this particular statement.
*/
static inline ulong get_max_execution_time(THD *thd) {
return (thd->lex->max_execution_time ? thd->lex->max_execution_time
: thd->variables.max_execution_time);
}
/**
Check whether max statement time is applicable to statement or not.
@param thd Thread (session) context.
@return true if max statement time is applicable to statement
@return false otherwise.
*/
static inline bool is_timer_applicable_to_statement(THD *thd) {
/*
The following conditions must be met:
- is SELECT statement.
- timer support is implemented and it is initialized.
- statement is not made by the slave threads.
- timer is not set for statement
- timer out value of is set
- SELECT statement is not from any stored programs.
*/
return (thd->lex->sql_command == SQLCOM_SELECT &&
(have_statement_timeout == SHOW_OPTION_YES) && !thd->slave_thread &&
!thd->timer &&
(thd->lex->max_execution_time || thd->variables.max_execution_time) &&
!thd->sp_runtime_ctx);
}
/**
Set the time until the currently running statement is aborted.
@param thd Thread (session) context.
@return true if the timer was armed.
*/
bool set_statement_timer(THD *thd) {
const ulong max_execution_time = get_max_execution_time(thd);
/**
whether timer can be set for the statement or not should be checked before
calling set_statement_timer function.
*/
assert(is_timer_applicable_to_statement(thd) == true);
assert(thd->timer == nullptr);
thd->timer = thd_timer_set(thd, thd->timer_cache, max_execution_time);
thd->timer_cache = nullptr;
if (thd->timer) {
thd->status_var.max_execution_time_set++;
global_aggregated_stats.get_shard(thd->thread_id())
.max_execution_time_set++;
} else {
thd->status_var.max_execution_time_set_failed++;
global_aggregated_stats.get_shard(thd->thread_id())
.max_execution_time_set_failed++;
}
return thd->timer;
}
/**
Deactivate the timer associated with the statement that was executed.
@param thd Thread (session) context.
*/
void reset_statement_timer(THD *thd) {
assert(thd->timer);
/* Cache the timer object if it can be reused. */
thd->timer_cache = thd_timer_reset(thd->timer);
thd->timer = nullptr;
}
/**
* Checks if a query reads a column that is _not_ available in the secondary
* engine (i.e. a column defined with NOT SECONDARY).
*
* @param lex Parse tree descriptor.
*
* @return True if at least one of the read columns is not in the secondary
* engine, false otherwise.
*/
bool reads_not_secondary_columns(const LEX *lex) {
// Check all read base tables.
const Table_ref *tl = lex->query_tables;
// For INSERT INTO SELECT statements, the table to insert into does not have
// to have a secondary engine. This table is always first in the list.
if (lex->sql_command == SQLCOM_INSERT_SELECT && tl != nullptr)
tl = tl->next_global;
for (; tl != nullptr; tl = tl->next_global) {
if (tl->is_placeholder()) continue;
// Check all read columns of table.
for (unsigned int i = bitmap_get_first_set(tl->table->read_set);
i != MY_BIT_NONE; i = bitmap_get_next_set(tl->table->read_set, i)) {
if (tl->table->field[i]->is_flag_set(NOT_SECONDARY_FLAG)) {
Opt_trace_context *trace = &lex->thd->opt_trace;
if (trace->is_started()) {
std::string message("");
message.append("Column ");
message.append(tl->table->field[i]->field_name);
message.append(" is marked as NOT SECONDARY.");
const Opt_trace_object trace_wrapper(trace);
Opt_trace_object oto(trace, "secondary_engine_not_used");
oto.add_alnum("reason", message.c_str());
}
return true;
}
}
}
return false;
}
static bool has_secondary_engine_defined(const LEX *lex) {
for (const Table_ref *tl = lex->query_tables; tl != nullptr;
tl = tl->next_global) {
if (tl == nullptr || tl->table == nullptr || tl->table->s == nullptr ||
!tl->table->s->has_secondary_engine()) {
return false;
}
}
return (lex->table_count > 0);
}
// Compare two engine names using the system collation.
static bool equal_engines(const LEX_CSTRING &engine1,
const LEX_CSTRING &engine2) {
return system_charset_info->coll->strnncollsp(
system_charset_info,
pointer_cast<const unsigned char *>(engine1.str), engine1.length,
pointer_cast<const unsigned char *>(engine2.str),
engine2.length) == 0;
}
// Helper function that checks if the command is eligible for secondary engine
// and if that's true returns the name of that eligible secondary storage
// engine.
const MYSQL_LEX_CSTRING *get_eligible_secondary_engine_from(const LEX *lex) {
// Don't use secondary storage engines for statements that call stored
// routines.
if (lex->uses_stored_routines()) return nullptr;
// Now check if the opened tables are available in a secondary
// storage engine. Only use the secondary tables if all the tables
// have a secondary tables, and they are all in the same secondary
// storage engine.
const LEX_CSTRING *secondary_engine = nullptr;
const Table_ref *tl = lex->query_tables;
if (lex->sql_command == SQLCOM_INSERT_SELECT && tl != nullptr) {
// If table from Table_ref is either view or derived table then
// do not perform INSERT AS SELECT.
if (tl->is_view_or_derived()) return nullptr;
// For INSERT INTO SELECT statements, the table to insert into does not have
// to have a secondary engine. This table is always first in the list.
tl = tl->next_global;
}
for (; tl != nullptr; tl = tl->next_global) {
// Schema tables are not available in secondary engines.
if (tl->schema_table != nullptr) return nullptr;
// We're only interested in base tables.
if (tl->is_placeholder()) continue;
// check if required pointers are valid before proceeding further
if (tl->table == nullptr || tl->table->s == nullptr) continue;
assert(!tl->table->s->is_secondary_engine());
// Give up, if the table is not in a secondary engine,
if (!tl->table->s->has_secondary_engine()) return nullptr;
if (secondary_engine == nullptr) {
// First base table. Save its secondary engine name for later.
secondary_engine = &tl->table->s->secondary_engine;
} else if (!equal_engines(*secondary_engine,
tl->table->s->secondary_engine)) {
// In a different secondary engine than the previous base tables.
return nullptr;
}
}
return secondary_engine;
}
const handlerton *get_secondary_engine_handlerton(const LEX *lex) {
if (const handlerton *hton = lex->m_sql_cmd->secondary_engine();
hton != nullptr) {
return hton;
}
const LEX_CSTRING *storage_engine = get_eligible_secondary_engine_from(lex);
if (storage_engine != nullptr) {
plugin_ref ref = ha_resolve_by_name(lex->thd, storage_engine, false);
if (ref != nullptr) {
return plugin_data<handlerton *>(ref);
}
}
return nullptr;
}
std::string_view get_secondary_engine_fail_reason(const LEX *lex) {
const auto *hton = get_secondary_engine_handlerton(lex);
if (hton != nullptr &&
hton->get_secondary_engine_offload_or_exec_fail_reason != nullptr &&
lex->thd->is_secondary_engine_forced()) {
return hton->get_secondary_engine_offload_or_exec_fail_reason(lex->thd);
}
return {};
}
std::string_view find_secondary_engine_fail_reason(const LEX *lex) {
const auto *hton = get_secondary_engine_handlerton(lex);
if (hton != nullptr &&
hton->find_secondary_engine_offload_fail_reason != nullptr &&
lex->thd->variables.use_secondary_engine == SECONDARY_ENGINE_FORCED) {
return hton->find_secondary_engine_offload_fail_reason(lex->thd);
}
if (hton == nullptr && get_eligible_secondary_engine_from(lex) != nullptr &&
get_eligible_secondary_engine_from(lex)->length > 0 &&
(native_strncasecmp(get_eligible_secondary_engine_from(lex)->str, "MOCK",
4) == 0)) {
// We don't support secondary storage engine execution,
// if it is a MOCK secondary engine.
return "Queries cannot be offloaded to a MOCK secondary engine";
}
// return a generic offload error if no specific reason is known
return "All plans were rejected by the secondary storage engine";
}
static bool set_secondary_engine_fail_reason(const LEX *lex,
std::string_view reason) {
const auto *hton = get_secondary_engine_handlerton(lex);
if (hton != nullptr &&
hton->set_secondary_engine_offload_fail_reason != nullptr &&
lex->thd->is_secondary_engine_forced()) {
hton->set_secondary_engine_offload_fail_reason(lex->thd, reason);
return true;
}
return false;
}
void set_fail_reason_and_raise_error(const LEX *lex, std::string_view reason) {
assert(!reason.empty());
if (set_secondary_engine_fail_reason(lex, reason)) {
my_error(ER_SECONDARY_ENGINE, MYF(0),
(std::data(get_secondary_engine_fail_reason(lex))));
} else {
std::string err_msg{"Reason: "};
err_msg.append("\"");
err_msg.append(std::data(reason));
err_msg.append("\"");
my_error(ER_SECONDARY_ENGINE, MYF(0), err_msg.c_str());
}
}
void find_and_set_offload_fail_reason(const LEX *lex) {
// If we are unable to gather secondary-engine-specific error message,
// check known unsupported features and raise a specific offload error.
std::string_view err_msg{};
if (lex->uses_stored_routines() ||
(lex->m_sql_cmd != nullptr && lex->m_sql_cmd->is_part_of_sp()) ||
lex->thd->sp_runtime_ctx != nullptr) {
// We don't support secondary storage engine execution,
// if the query has statements that call stored routines.
err_msg =
"Queries part of stored functions or calling stored functions are not "
"supported in secondary engines";
} else if (!has_secondary_engine_defined(lex)) {
// We don't support secondary storage engine execution,
// if at least one of the query tables have no secondary engine defined.
err_msg =
"No secondary engine defined for at least one of the query tables";
} else {
err_msg = find_secondary_engine_fail_reason(lex);
}
assert(!err_msg.empty());
set_fail_reason_and_raise_error(lex, err_msg);
}
bool validate_use_secondary_engine(const LEX *lex) {
if (lex->m_sql_cmd == nullptr) {
return false;
}
THD *thd = lex->thd;
const Sql_cmd *sql_cmd = lex->m_sql_cmd;
// Ensure that all read columns are in the secondary engine.
if (sql_cmd->using_secondary_storage_engine()) {
if (reads_not_secondary_columns(lex)) {
std::string_view err_msg = find_secondary_engine_fail_reason(lex);
assert(!err_msg.empty());
set_fail_reason_and_raise_error(lex, err_msg);
return true;
}
return false;
}
if (thd->secondary_engine_optimization() ==
Secondary_engine_optimization::SECONDARY &&
thd->is_secondary_engine_forced()) {
// Gather secondary-engine-specific error message.
std::string_view offloadfail_reason = get_secondary_engine_fail_reason(lex);
if (!offloadfail_reason.empty()) {
if (thd->is_error()) {
thd->clear_error();
}
my_error(ER_SECONDARY_ENGINE, MYF(0), std::data(offloadfail_reason));
return true;
}
// If we haven't generated a specific error so far,
// we try to generate one here.
if (!thd->is_error()) {
find_and_set_offload_fail_reason(lex);
return true;
}
}
return false;
}
bool Sql_cmd_dml::prepare(THD *thd) {
DBUG_TRACE;
bool error_handler_active = false;
Ignore_error_handler ignore_handler;
Strict_error_handler strict_handler;
// @todo: Move this to constructor?
lex = thd->lex;
// Parser may have assigned a specific query result handler
result = lex->result;
assert(!is_prepared());
assert(!lex->unit->is_prepared() && !lex->unit->is_optimized() &&
!lex->unit->is_executed());
/*
Constant folding could cause warnings during preparation. Make
sure they are promoted to errors when strict mode is enabled.
*/
if (is_data_change_stmt() && needs_explicit_preparation()) {
// Push ignore / strict error handler
if (lex->is_ignore()) {
thd->push_internal_handler(&ignore_handler);
error_handler_active = true;
} else if (thd->is_strict_mode()) {
thd->push_internal_handler(&strict_handler);
error_handler_active = true;
}
}
// Perform a coarse statement-specific privilege check.
if (precheck(thd)) goto err;
// Trigger out_of_memory condition inside open_tables_for_query()
DBUG_EXECUTE_IF("sql_cmd_dml_prepare__out_of_memory",
DBUG_SET("+d,simulate_out_of_memory"););
/*
Open tables and expand views.
During prepare of query (not as part of an execute), acquire only
S metadata locks instead of SW locks to be compatible with concurrent
LOCK TABLES WRITE and global read lock.
*/
if (open_tables_for_query(
thd, lex->query_tables,
needs_explicit_preparation() ? MYSQL_OPEN_FORCE_SHARED_MDL : 0)) {
if (thd->is_error()) // @todo - dictionary code should be fixed
goto err;
if (error_handler_active) thd->pop_internal_handler();
lex->cleanup(false);
return true;
}
DEBUG_SYNC(thd, "after_open_tables");
#ifndef NDEBUG
if (sql_command_code() == SQLCOM_SELECT) DEBUG_SYNC(thd, "after_table_open");
#endif
lex->set_using_hypergraph_optimizer(
thd->optimizer_switch_flag(OPTIMIZER_SWITCH_HYPERGRAPH_OPTIMIZER));
if (thd->lex->validate_use_in_old_optimizer()) {
return true;
}
if (lex->set_var_list.elements && resolve_var_assignments(thd, lex))
goto err; /* purecov: inspected */
{
const Prepare_error_tracker tracker(thd);
const Prepared_stmt_arena_holder ps_arena_holder(thd);
const Enable_derived_merge_guard derived_merge_guard(
thd, is_show_cmd_using_system_view(thd));
if (prepare_inner(thd)) goto err;
if (needs_explicit_preparation() && result != nullptr) {
result->cleanup();
}
if (!is_regular()) {
if (save_cmd_properties(thd)) goto err;
}
if (needs_explicit_preparation()) {
lex->set_secondary_engine_execution_context(nullptr);
}
set_prepared();
}
// Pop ignore / strict error handler
if (error_handler_active) thd->pop_internal_handler();
// Revertable changes are not supported during preparation
assert(thd->change_list.is_empty());
return false;
err:
assert(thd->is_error());
DBUG_PRINT("info", ("report_error: %d", thd->is_error()));
lex->set_secondary_engine_execution_context(nullptr);
if (error_handler_active) thd->pop_internal_handler();
if (result != nullptr) result->cleanup();
lex->cleanup(false);
return true;
}
bool Sql_cmd_select::accept(THD *thd, Select_lex_visitor *visitor) {
return thd->lex->unit->accept(visitor);
}
const MYSQL_LEX_CSTRING *Sql_cmd_select::eligible_secondary_storage_engine(
THD *thd) const {
return get_eligible_secondary_engine(thd);
}
/**
Prepare a SELECT statement.
*/
bool Sql_cmd_select::prepare_inner(THD *thd) {
if (lex->is_explain()) {
/*
Always use Query_result_send for EXPLAIN, even if it's an EXPLAIN for
SELECT ... INTO OUTFILE: a user application should be able to prepend
EXPLAIN to any query and receive output for it, even if the query itself
redirects the output.
*/
result = new (thd->mem_root) Query_result_send();
if (result == nullptr) return true; /* purecov: inspected */
} else {
if (result == nullptr) {
if (sql_command_code() == SQLCOM_SELECT)
result = new (thd->mem_root) Query_result_send();
else if (sql_command_code() == SQLCOM_DO)
result = new (thd->mem_root) Query_result_do();
else // Currently assumed to be a SHOW command
result = new (thd->mem_root) Query_result_send();
if (result == nullptr) return true; /* purecov: inspected */
}
}
Query_expression *const unit = lex->unit;
Query_block *parameters = unit->global_parameters();
if (!parameters->has_limit()) {
parameters->m_use_select_limit = true;
}
if (unit->is_simple()) {
Query_block *const select = unit->first_query_block();
select->context.resolve_in_select_list = true;
select->set_query_result(result);
unit->set_query_result(result);
// Unlock the table as soon as possible, so don't set SELECT_NO_UNLOCK.
select->make_active_options(0, 0);
if (select->prepare(thd, nullptr)) return true;
unit->set_prepared();
} else {
// If we have multiple query blocks, don't unlock and re-lock
// tables between each each of them.
if (unit->prepare(thd, result, nullptr, SELECT_NO_UNLOCK, 0)) return true;
}
return false;
}
bool has_external_table(const LEX *lex) {
if (lex->m_sql_cmd == nullptr) {
return false;
}
for (Table_ref *ref = lex->query_tables; ref != nullptr;
ref = ref->next_global) {
if (ref->is_external()) {
return true;
}
}
return false;
}
bool Sql_cmd_dml::execute(THD *thd) {
DBUG_TRACE;
lex = thd->lex;
Query_expression *const unit = lex->unit;
bool statement_timer_armed = false;
bool error_handler_active = false;
Ignore_error_handler ignore_handler;
Strict_error_handler strict_handler;
// If statement is preparable, it must be prepared
assert(owner() == nullptr || is_prepared());
// If statement is regular, it must be unprepared
assert(!is_regular() || !is_prepared());
// If statement is part of SP, it can be both prepared and unprepared.
// If a timer is applicable to statement, then set it.
if (is_timer_applicable_to_statement(thd))
statement_timer_armed = set_statement_timer(thd);
if (is_data_change_stmt()) {
// Push ignore / strict error handler
if (lex->is_ignore()) {
thd->push_internal_handler(&ignore_handler);
error_handler_active = true;
/*
UPDATE IGNORE can be unsafe. We therefore use row based
logging if mixed or row based logging is available.
TODO: Check if the order of the output of the select statement is
deterministic. Waiting for BUG#42415
*/
if (lex->sql_command == SQLCOM_UPDATE)
lex->set_stmt_unsafe(LEX::BINLOG_STMT_UNSAFE_UPDATE_IGNORE);
} else if (thd->is_strict_mode()) {
thd->push_internal_handler(&strict_handler);
error_handler_active = true;
}
}
if (!is_prepared()) {
if (prepare(thd)) goto err;
} else {
/*
Prepared statement, open tables referenced in statement and check
privileges for it.
*/
cleanup(thd);
if (open_tables_for_query(thd, lex->query_tables, 0)) goto err;
#ifndef NDEBUG
if (sql_command_code() == SQLCOM_SELECT)
DEBUG_SYNC(thd, "after_table_open");
#endif
// Use the hypergraph optimizer for the SELECT statement, if enabled.
const bool need_hypergraph_optimizer =
thd->optimizer_switch_flag(OPTIMIZER_SWITCH_HYPERGRAPH_OPTIMIZER);
if (need_hypergraph_optimizer != lex->using_hypergraph_optimizer() &&
ask_to_reprepare(thd)) {
goto err;
}
assert(need_hypergraph_optimizer == lex->using_hypergraph_optimizer());
// Bind table and field information
if (restore_cmd_properties(thd)) goto err;
if (check_privileges(thd)) goto err;
if (m_lazy_result) {
const Prepared_stmt_arena_holder ps_arena_holder(thd);
if (result->prepare(thd, *unit->get_unit_column_types(), unit)) goto err;
m_lazy_result = false;
}
}
if (validate_use_secondary_engine(lex)) goto err;
lex->set_exec_started();
DBUG_EXECUTE_IF("use_attachable_trx",
thd->begin_attachable_ro_transaction(););
THD_STAGE_INFO(thd, stage_init);
thd->clear_current_query_costs();
// Replication may require extra check of data change statements
if (is_data_change_stmt() && run_before_dml_hook(thd)) goto err;
// Revertable changes are not supported during preparation
assert(thd->change_list.is_empty());
assert(!lex->is_query_tables_locked());
/*
Locking of tables is done after preparation but before optimization.
This allows to do better partition pruning and avoid locking unused
partitions. As a consequence, in such a case, prepare stage can rely only
on metadata about tables used and not data from them.
*/
if (!is_empty_query()) {
if (lock_tables(thd, lex->query_tables, lex->table_count, 0)) goto err;
}
// Perform statement-specific execution
if (execute_inner(thd)) goto err;
// Count the number of statements offloaded to a secondary storage engine.
if (using_secondary_storage_engine() && lex->unit->is_executed()) {
++thd->status_var.secondary_engine_execution_count;
global_aggregated_stats.get_shard(thd->thread_id())
.secondary_engine_execution_count++;
}
assert(!thd->is_error());
// Pop ignore / strict error handler
if (error_handler_active) thd->pop_internal_handler();
THD_STAGE_INFO(thd, stage_end);
// Do partial cleanup (preserve plans for EXPLAIN).
lex->cleanup(false);
lex->clear_values_map();
lex->set_secondary_engine_execution_context(nullptr);
// Perform statement-specific cleanup for Query_result
if (result != nullptr) result->cleanup();
thd->save_current_query_costs();
thd->update_previous_found_rows();
DBUG_EXECUTE_IF("use_attachable_trx", thd->end_attachable_transaction(););
if (statement_timer_armed && thd->timer) reset_statement_timer(thd);
/*
This sync point is normally right before thd->query_plan is reset, so
EXPLAIN FOR CONNECTION can catch the plan. It is copied here as
after unprepare() EXPLAIN considers the query as "not ready".
@todo remove in WL#6570 when unprepare() is gone.
*/
DEBUG_SYNC(thd, "before_reset_query_plan");
return false;
err:
assert(thd->is_error() || thd->killed);
DBUG_PRINT("info", ("report_error: %d", thd->is_error()));
THD_STAGE_INFO(thd, stage_end);
lex->cleanup(false);
lex->clear_values_map();
lex->set_secondary_engine_execution_context(nullptr);
// Abort and cleanup the result set (if it has been prepared).
if (result != nullptr) {
result->abort_result_set(thd);
result->cleanup();
}
if (error_handler_active) thd->pop_internal_handler();
if (statement_timer_armed && thd->timer) reset_statement_timer(thd);
/*
There are situations where we want to know the cost of a query that
has failed during execution, e.g because of a timeout.
*/
thd->save_current_query_costs();
DBUG_EXECUTE_IF("use_attachable_trx", thd->end_attachable_transaction(););
return thd->is_error();
}
void accumulate_statement_cost(const LEX *lex) {
Opt_trace_context *trace = &lex->thd->opt_trace;
const Opt_trace_disable_I_S disable_trace(trace, true);
double total_cost = 0.0;
for (const Query_block *query_block = lex->all_query_blocks_list;
query_block != nullptr;
query_block = query_block->next_select_in_list()) {
if (query_block->join == nullptr) continue;
// Get the cost of this query block.
double query_block_cost = query_block->join->best_read;
// If it is a non-cacheable subquery, estimate how many times it
// needs to be executed, and adjust the cost accordingly.
const Item_subselect *item = query_block->master_query_expression()->item;
if (item != nullptr && !query_block->is_cacheable())
query_block_cost *= calculate_subquery_executions(item, trace);
total_cost += query_block_cost;
}
lex->thd->m_current_query_cost = total_cost;
}
namespace {
/**
Gets the secondary storage engine pre prepare hook function, if any. If no
hook is found, this function returns false. If hook function is found, it
returns the return value of the hook. Please refer to
secondary_engine_pre_prepare_hook_t definition for description of its return
value.
*/
bool SecondaryEngineCallPrePrepareHook(THD *thd,
const LEX_CSTRING &secondary_engine) {
handlerton *hton = nullptr;
plugin_ref ref = ha_resolve_by_name(thd, &secondary_engine, false);
if (ref != nullptr) {
hton = plugin_data<handlerton *>(ref);
}
if (hton != nullptr) {
secondary_engine_pre_prepare_hook_t secondary_engine_pre_prepare_hook =
hton->secondary_engine_pre_prepare_hook;
if (secondary_engine_pre_prepare_hook != nullptr) {
return secondary_engine_pre_prepare_hook(thd);
}
}
return false;
}
} // namespace
/**
Checks if a query should be retried using a secondary storage engine.
@param thd the current session
@retval true if the statement should be retried in a secondary engine
@retval false if the statement should not be retried
*/
static bool retry_with_secondary_engine(THD *thd) {
// Only retry if the current statement is being tentatively
// optimized for the primary engine.
if (thd->secondary_engine_optimization() !=
Secondary_engine_optimization::PRIMARY_TENTATIVELY)
return false;
Sql_cmd *const sql_cmd = thd->lex->m_sql_cmd;
assert(!sql_cmd->using_secondary_storage_engine());
// Don't retry if there is a property of the statement that prevents use of
// secondary engines.
const LEX_CSTRING *secondary_engine =
thd->lex->m_sql_cmd->eligible_secondary_storage_engine(thd);
if (secondary_engine == nullptr) {
sql_cmd->disable_secondary_storage_engine();
return false;
}
// Don't retry if it's already determined that the statement should not be
// executed by a secondary engine.
if (sql_cmd->secondary_storage_engine_disabled()) {
return false;
}
// Don't retry if there is a property of the environment that prevents use of
// secondary engines.
if (!thd->is_secondary_storage_engine_eligible()) {
return false;
}
// If the query cannot be executed in the PRIMARY engine, always attempt to
// execute it in the secondary engine whenever possible.
if (thd->lex->can_execute_only_in_secondary_engine()) {
return true;
}
return SecondaryEngineCallPrePrepareHook(thd, *secondary_engine);
}
bool optimize_secondary_engine(THD *thd) {
if (retry_with_secondary_engine(thd)) {
// NOLINTNEXTLINE(cppcoreguidelines-avoid-do-while)
DBUG_EXECUTE_IF("emulate_user_query_kill", {
thd->get_stmt_da()->set_error_status(thd, ER_QUERY_INTERRUPTED);
return true;
});
thd->get_stmt_da()->reset_diagnostics_area();
thd->get_stmt_da()->set_error_status(thd, ER_PREPARE_FOR_SECONDARY_ENGINE);
return true;
}
if (thd->secondary_engine_optimization() ==
Secondary_engine_optimization::PRIMARY_TENTATIVELY &&
thd->lex->m_sql_cmd != nullptr &&
thd->lex->m_sql_cmd->is_optional_transform_prepared()) {
// A previous preparation did a secondary engine specific transform,
// and this transform wasn't requested for the primary engine (in
// 'optimizer_switch'), so in this new execution we need to reprepare for
// the primary engine without the optional transform, for likely better
// performance.
thd->lex->m_sql_cmd->set_optional_transform_prepared(false);
thd->get_stmt_da()->reset_diagnostics_area();
thd->get_stmt_da()->set_error_status(thd, ER_PREPARE_FOR_PRIMARY_ENGINE);
return true;
}
const handlerton *secondary_engine = thd->lex->m_sql_cmd->secondary_engine();
/* When there is a secondary engine hook, return its return value,
* otherwise return false (success). */
return secondary_engine != nullptr &&
secondary_engine->optimize_secondary_engine != nullptr &&
secondary_engine->optimize_secondary_engine(thd, thd->lex);
}
void notify_plugins_after_select(THD *thd, const Sql_cmd *cmd) {
/* Return if one of the 2 conditions is true:
* 1. when secondary engine statement context is not present, query cost is
* lower than the secondary than the engine threshold.
* 2. When secondary engine statement context is present, primary engine
* is the better execution engine for this query.
* This prevents calling plugin_foreach for short queries, reducing the
* overhead. */
if (((thd->secondary_engine_statement_context() == nullptr) &&
thd->m_current_query_cost <=
thd->variables.secondary_engine_cost_threshold) ||
((thd->secondary_engine_statement_context() != nullptr) &&
thd->secondary_engine_statement_context()
->is_primary_engine_optimal())) {
return;
}
auto executed_in = (cmd != nullptr && cmd->using_secondary_storage_engine())
? SelectExecutedIn::kSecondaryEngine
: SelectExecutedIn::kPrimaryEngine;
plugin_foreach(
thd,
[](THD *t, plugin_ref plugin, void *arg) -> bool {
handlerton *hton = plugin_data<handlerton *>(plugin);
if (hton->notify_after_select != nullptr) {
hton->notify_after_select(t, *(static_cast<SelectExecutedIn *>(arg)));
}
return false;
},
MYSQL_STORAGE_ENGINE_PLUGIN, &executed_in);
}
/**
Execute a DML statement.
This is the default implementation for a DML statement and uses a
nested-loop join processor per outer-most query block.
The implementation is split in two: One for query expressions containing
a single query block and one for query expressions containing multiple
query blocks combined with UNION.
*/
bool Sql_cmd_dml::execute_inner(THD *thd) {
Query_expression *unit = lex->unit;
if (unit->optimize(thd, /*materialize_destination=*/nullptr,
/*create_iterators=*/true, /*finalize_access_paths=*/true))
return true;
// Calculate the current statement cost.
accumulate_statement_cost(lex);
// Perform secondary engine optimizations, if needed.
if (optimize_secondary_engine(thd)) return true;
// We know by now that execution will complete (successful or with error)
lex->set_exec_completed();
if (lex->is_explain()) {
for (Table_ref *ref = lex->query_tables; ref != nullptr;
ref = ref->next_global) {
if (ref->table != nullptr && ref->table->file != nullptr) {
handlerton *hton = ref->table->file->ht;
if (hton->external_engine_explain_check != nullptr) {
if (hton->external_engine_explain_check(thd)) return true;
}
}
}
if (explain_query(thd, thd, unit)) return true; /* purecov: inspected */
} else {
if (unit->execute(thd)) return true;
notify_plugins_after_select(thd, lex->m_sql_cmd);
}
return false;
}
bool Sql_cmd_dml::restore_cmd_properties(THD *thd) {
lex->restore_cmd_properties();
bind_fields(thd->stmt_arena->item_list());
return false;
}
bool Sql_cmd_dml::save_cmd_properties(THD *thd) {
return lex->save_cmd_properties(thd);
}
Query_result *Sql_cmd_dml::query_result() const {
assert(is_prepared());
return lex->unit->query_result() != nullptr
? lex->unit->query_result()
: lex->unit->first_query_block()->query_result();
}
void Sql_cmd_dml::set_query_result(Query_result *result_arg) {
result = result_arg;
Query_expression *unit = lex->unit;
unit->query_term()->query_block()->set_query_result(result);
unit->set_query_result(result);
}
/**
Performs access check for the locking clause, if present.
@param thd Current session, used for checking access and raising error.
@param tables Tables in the query's from clause.
@retval true There was a locking clause and access was denied. An error has
been raised.
@retval false There was no locking clause or access was allowed to it. This
is always returned in an embedded build.
*/
static bool check_locking_clause_access(THD *thd, Global_tables_list tables) {
for (Table_ref *table_ref : tables)
if (table_ref->lock_descriptor().type == TL_WRITE) { // i.e. FOR UPDATE
bool access_is_granted = false;
/*
If either of these privileges is present along with SELECT, access is
granted.
*/
for (Access_bitmask allowed_priv :
{UPDATE_ACL, DELETE_ACL, LOCK_TABLES_ACL}) {
Access_bitmask priv = SELECT_ACL | allowed_priv;
if (!check_table_access(thd, priv, table_ref, false, 1, true)) {
access_is_granted = true;
// No need to check for other privileges for this table.
// However, we still need to check privileges for other tables.
break;
}
}
if (!access_is_granted) {
const Security_context *sctx = thd->security_context();
my_error(ER_TABLEACCESS_DENIED_ERROR, MYF(0),
"SELECT with locking clause", sctx->priv_user().str,
sctx->host_or_ip().str, table_ref->get_table_name());
return true;
}
}
return false;
}
/**
Perform an authorization precheck for an unprepared SELECT statement.
This function will check that we have some privileges to all involved tables
of the query (and possibly to other entities).
*/
bool Sql_cmd_select::precheck(THD *thd) {
/*
lex->exchange != NULL implies SELECT .. INTO OUTFILE and this
requires FILE_ACL access.
*/
const bool check_file_acl =
(lex->result != nullptr && lex->result->needs_file_privilege());
/*
Check following,
1) Check FILE privileges for current user who runs a query if needed.
2) Check privileges for every user specified as a definer for a view or
check privilege to access any DB in case a table wasn't specified.
Although calling of check_access() when no tables are specified results
in returning false value immediately, this call has important side
effect: the counter 'stage/sql/checking permissions' in performance
schema is incremented. Therefore, this function is called in order to
save backward compatibility.
3) Performs access check for the locking clause, if present.
*/
Table_ref *tables = lex->query_tables;
if (check_file_acl && check_global_access(thd, FILE_ACL)) return true;
bool res;
if (tables)
res = check_table_access(thd, SELECT_ACL, tables, false, UINT_MAX, false);
else
res = check_access(thd, SELECT_ACL, any_db, nullptr, nullptr, false, false);
return res || check_locking_clause_access(thd, Global_tables_list(tables));
}
/**
Perform an authorization check for a prepared SELECT statement.
*/
bool Sql_cmd_select::check_privileges(THD *thd) {
/*
lex->exchange != nullptr implies SELECT .. INTO OUTFILE and this
requires FILE_ACL access.
*/
if (result->needs_file_privilege() &&
check_access(thd, FILE_ACL, any_db, nullptr, nullptr, false, false))
return true;
if (check_all_table_privileges(thd)) return true;
if (check_locking_clause_access(thd, Global_tables_list(lex->query_tables)))
return true;
Query_expression *const unit = lex->unit;
for (auto qt : unit->query_terms<>())
if (qt->query_block()->check_column_privileges(thd)) return true;
return false;
}
bool Sql_cmd_dml::check_all_table_privileges(THD *thd) {
// Check for all possible DML privileges
const Table_ref *const first_not_own_table = thd->lex->first_not_own_table();
for (Table_ref *tr = lex->query_tables; tr != first_not_own_table;
tr = tr->next_global) {
if (tr->is_internal()) // No privilege check required for internal tables
continue;
// Calculated wanted privilege based on how table/view is used:
Access_bitmask want_privilege = 0;
if (tr->is_inserted()) {
want_privilege |= INSERT_ACL;
}
if (tr->is_updated()) {
want_privilege |= UPDATE_ACL;
}
if (tr->is_deleted()) {
want_privilege |= DELETE_ACL;
}
if (want_privilege == 0) {
want_privilege = SELECT_ACL;
}
if (tr->referencing_view == nullptr) {
// This is a base table
if (check_single_table_access(thd, want_privilege, tr, false))
return true;
} else {
// This is a view, set handler for transformation of errors
Internal_error_handler_holder<View_error_handler, Table_ref> view_handler(
thd, true, tr);
for (Table_ref *t = tr; t->referencing_view; t = t->referencing_view) {
if (check_single_table_access(thd, want_privilege, t, false))
return true;
}
}
}
return false;
}
const MYSQL_LEX_CSTRING *Sql_cmd_dml::get_eligible_secondary_engine(
THD *thd) const {
return get_eligible_secondary_engine_from(thd->lex);
}
/*****************************************************************************
Check fields, find best join, do the select and output fields.
All tables must be opened.
*****************************************************************************/
/**
@brief Check if two items are compatible wrt. materialization.
@param outer Expression from outer query
@param inner Expression from inner query
@retval true If subquery types allow materialization.
@retval false Otherwise.
@note the purpose is similar to that of comparable_in_index().
*/
bool types_allow_materialization(Item *outer, Item *inner) {
auto res_outer = outer->result_type();
auto res_inner = inner->result_type();
// Materialization of rows nested inside rows is not currently supported.
if (res_outer == ROW_RESULT || res_inner == ROW_RESULT) return false;
const bool num_outer = res_outer == INT_RESULT || res_outer == REAL_RESULT ||
res_outer == DECIMAL_RESULT;
const bool num_inner = res_inner == INT_RESULT || res_inner == REAL_RESULT ||
res_inner == DECIMAL_RESULT;
/*
Materialization uses index lookup which implicitly converts the type of
res_outer into that of res_inner.
However, this can be done only if it respects rules in:
https://dev.mysql.com/doc/refman/8.0/en/type-conversion.html
https://dev.mysql.com/doc/refman/8.0/en/date-and-time-type-conversion.html
Those rules say that, generally, if types differ, we convert them to
REAL.
So, looking up into a number is ok: outer will be converted to
number. Collations don't matter.
This covers e.g. looking up INT into DECIMAL, CHAR into INT, DECIMAL into
BIT.
*/
if (num_inner) return true;
// Conversely, looking up one number into a non-number is not possible.
if (num_outer) return false;
/*
Arguments are strings or temporal.
Require same collation for correct comparison.
*/
assert(res_outer == STRING_RESULT && res_inner == STRING_RESULT);
if (outer->collation.collation != inner->collation.collation) return false;
const bool temp_outer = outer->is_temporal();
const bool temp_inner = inner->is_temporal();
/*
Same logic as for numbers.
As explained in add_key_field(), IndexedTimeComparedToDate is not working;
see also field_time_cmp_date().
@todo unify all pieces of code which deal with this same problem.
*/
if (temp_inner) {
if (!inner->is_temporal_with_date())
return temp_outer && !outer->is_temporal_with_date();
return true;
}
if (temp_outer) return false;
return true;
}
/*
Check if the table's rowid is included in the temptable
SYNOPSIS
sj_table_is_included()
join The join
join_tab The table to be checked
DESCRIPTION
SemiJoinDuplicateElimination: check the table's rowid should be included
in the temptable. This is so if
1. The table is not embedded within some semi-join nest
2. The has been pulled out of a semi-join nest, or
3. The table is functionally dependent on some previous table
[4. This is also true for constant tables that can't be
NULL-complemented but this function is not called for such tables]
RETURN
true - Include table's rowid
false - Don't
*/
static bool sj_table_is_included(JOIN *join, JOIN_TAB *join_tab) {
if (join_tab->emb_sj_nest) return false;
/* Check if this table is functionally dependent on the tables that
are within the same outer join nest
*/
Table_ref *embedding = join_tab->table_ref->embedding;
if (join_tab->type() == JT_EQ_REF) {
table_map depends_on = 0;
for (uint kp = 0; kp < join_tab->ref().key_parts; kp++)
depends_on |= join_tab->ref().items[kp]->used_tables();
for (size_t idx : BitsSetIn(depends_on & ~PSEUDO_TABLE_BITS)) {
JOIN_TAB *ref_tab = join->map2table[idx];
if (embedding != ref_tab->table_ref->embedding) return true;
}
/* Ok, functionally dependent */
return false;
}
/* Not functionally dependent => need to include*/
return true;
}
SJ_TMP_TABLE *create_sj_tmp_table(THD *thd, JOIN *join,
SJ_TMP_TABLE_TAB *first_tab,
SJ_TMP_TABLE_TAB *last_tab) {
uint jt_rowid_offset =
0; // # tuple bytes are already occupied (w/o NULL bytes)
uint jt_null_bits = 0; // # null bits in tuple bytes
for (SJ_TMP_TABLE_TAB *tab = first_tab; tab != last_tab; ++tab) {
QEP_TAB *qep_tab = tab->qep_tab;
tab->rowid_offset = jt_rowid_offset;
jt_rowid_offset += qep_tab->table()->file->ref_length;
if (qep_tab->table()->is_nullable()) {
tab->null_byte = jt_null_bits / 8;
tab->null_bit = jt_null_bits++;
}
qep_tab->table()->prepare_for_position();
}
SJ_TMP_TABLE *sjtbl;
if (jt_rowid_offset) /* Temptable has at least one rowid */
{
sjtbl = new (thd->mem_root) SJ_TMP_TABLE;
if (sjtbl == nullptr) return nullptr;
sjtbl->tabs =
thd->mem_root->ArrayAlloc<SJ_TMP_TABLE_TAB>(last_tab - first_tab);
if (sjtbl->tabs == nullptr) return nullptr;
sjtbl->tabs_end = std::uninitialized_copy(first_tab, last_tab, sjtbl->tabs);
sjtbl->is_confluent = false;
sjtbl->rowid_len = jt_rowid_offset;
sjtbl->null_bits = jt_null_bits;
sjtbl->null_bytes = (jt_null_bits + 7) / 8;
sjtbl->tmp_table = create_duplicate_weedout_tmp_table(
thd, sjtbl->rowid_len + sjtbl->null_bytes, sjtbl);
if (sjtbl->tmp_table == nullptr) return nullptr;
if (sjtbl->tmp_table->hash_field)
sjtbl->tmp_table->file->ha_index_init(0, false);
join->sj_tmp_tables.push_back(sjtbl->tmp_table);
} else {
/*
This is confluent case where the entire subquery predicate does
not depend on anything at all, ie this is
WHERE const IN (uncorrelated select)
*/
if (!(sjtbl = new (thd->mem_root) SJ_TMP_TABLE))
return nullptr; /* purecov: inspected */
sjtbl->tmp_table = nullptr;
sjtbl->is_confluent = true;
sjtbl->have_confluent_row = false;
}
return sjtbl;
}
/**
Setup the strategies to eliminate semi-join duplicates.
@param join Join to process
@param no_jbuf_after Do not use join buffering after the table with this
number
@retval false OK
@retval true Out of memory error
Setup the strategies to eliminate semi-join duplicates.
At the moment there are 5 strategies:
-# DuplicateWeedout (use of temptable to remove duplicates based on rowids
of row combinations)
-# FirstMatch (pick only the 1st matching row combination of inner tables)
-# LooseScan (scanning the sj-inner table in a way that groups duplicates
together and picking the 1st one)
-# MaterializeLookup (Materialize inner tables, then setup a scan over
outer correlated tables, lookup in materialized table)
-# MaterializeScan (Materialize inner tables, then setup a scan over
materialized tables, perform lookup in outer tables)
The join order has "duplicate-generating ranges", and every range is
served by one strategy or a combination of FirstMatch with with some
other strategy.
"Duplicate-generating range" is defined as a range within the join order
that contains all of the inner tables of a semi-join. All ranges must be
disjoint, if tables of several semi-joins are interleaved, then the ranges
are joined together, which is equivalent to converting
`SELECT ... WHERE oe1 IN (SELECT ie1 ...) AND oe2 IN (SELECT ie2 )`
to
`SELECT ... WHERE (oe1, oe2) IN (SELECT ie1, ie2 ... ...)`.
Applicability conditions are as follows:
@par DuplicateWeedout strategy
@code
(ot|nt)* [ it ((it|ot|nt)* (it|ot))] (nt)*
+------+ +=========================+ +---+
(1) (2) (3)
@endcode
-# Prefix of OuterTables (those that participate in IN-equality and/or are
correlated with subquery) and outer Non-correlated tables.
-# The handled range. The range starts with the first sj-inner table, and
covers all sj-inner and outer tables Within the range, Inner, Outer,
outer non-correlated tables may follow in any order.
-# The suffix of outer non-correlated tables.
@par FirstMatch strategy
@code
(ot|nt)* [ it (it)* ] (nt)*
+------+ +==========+ +---+
(1) (2) (3)
@endcode
-# Prefix of outer correlated and non-correlated tables
-# The handled range, which may contain only inner tables.
-# The suffix of outer non-correlated tables.
@par LooseScan strategy
@code
(ot|ct|nt) [ loosescan_tbl (ot|nt|it)* it ] (ot|nt)*
+--------+ +===========+ +=============+ +------+
(1) (2) (3) (4)
@endcode
-# Prefix that may contain any outer tables. The prefix must contain all
the non-trivially correlated outer tables. (non-trivially means that
the correlation is not just through the IN-equality).
-# Inner table for which the LooseScan scan is performed. Notice that
special requirements for existence of certain indexes apply to this
table, @see class Loose_scan_opt.
-# The remainder of the duplicate-generating range. It is served by
application of FirstMatch strategy. Outer IN-correlated tables must be
correlated to the LooseScan table but not to the inner tables in this
range. (Currently, there can be no outer tables in this range because
of implementation restrictions, @see
Optimize_table_order::advance_sj_state()).
-# The suffix of outer correlated and non-correlated tables.
@par MaterializeLookup strategy
@code
(ot|nt)* [ it (it)* ] (nt)*
+------+ +==========+ +---+
(1) (2) (3)
@endcode
-# Prefix of outer correlated and non-correlated tables.
-# The handled range, which may contain only inner tables.
The inner tables are materialized in a temporary table that is
later used as a lookup structure for the outer correlated tables.
-# The suffix of outer non-correlated tables.
@par MaterializeScan strategy
@code
(ot|nt)* [ it (it)* ] (ot|nt)*
+------+ +==========+ +-----+
(1) (2) (3)
@endcode
-# Prefix of outer correlated and non-correlated tables.
-# The handled range, which may contain only inner tables.
The inner tables are materialized in a temporary table which is
later used to setup a scan.
-# The suffix of outer correlated and non-correlated tables.
Note that MaterializeLookup and MaterializeScan has overlap in their
patterns. It may be possible to consolidate the materialization strategies
into one.
The choice between the strategies is made by the join optimizer (see
advance_sj_state() and fix_semijoin_strategies()). This function sets up
all fields/structures/etc needed for execution except for
setup/initialization of semi-join materialization which is done in
setup_materialized_table().
*/
static bool setup_semijoin_dups_elimination(JOIN *join, uint no_jbuf_after) {
uint tableno;
THD *thd = join->thd;
DBUG_TRACE;
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
if (join->query_block->sj_nests.empty()) return false;
QEP_TAB *const qep_array = join->qep_tab;
for (tableno = join->const_tables; tableno < join->primary_tables;) {
#ifndef NDEBUG
const bool tab_in_sj_nest = join->best_ref[tableno]->emb_sj_nest != nullptr;
#endif
QEP_TAB *const tab = &qep_array[tableno];
POSITION *const pos = tab->position();
if (pos->sj_strategy == SJ_OPT_NONE) {
tableno++; // nothing to do
continue;
}
QEP_TAB *last_sj_tab = tab + pos->n_sj_tables - 1;
switch (pos->sj_strategy) {
case SJ_OPT_MATERIALIZE_LOOKUP:
case SJ_OPT_MATERIALIZE_SCAN:
assert(false); // Should not occur among "primary" tables
// Do nothing
tableno += pos->n_sj_tables;
break;
case SJ_OPT_LOOSE_SCAN: {
assert(tab_in_sj_nest); // First table must be inner
/* We jump from the last table to the first one */
tab->match_tab = last_sj_tab->idx();
/* For LooseScan, duplicate elimination is based on rows being sorted
on key. We need to make sure that range select keeps the sorted index
order. (When using MRR it may not.)
Note: need_sorted_output() implementations for range select classes
that do not support sorted output, will trigger an assert. This
should not happen since LooseScan strategy is only picked if sorted
output is supported.
*/
if (tab->range_scan()) {
assert(used_index(tab->range_scan()) == pos->loosescan_key);
set_need_sorted_output(tab->range_scan());
}
const uint keyno = pos->loosescan_key;
assert(tab->keys().is_set(keyno));
tab->set_index(keyno);
/* Calculate key length */
uint keylen = 0;
for (uint kp = 0; kp < pos->loosescan_parts; kp++)
keylen += tab->table()->key_info[keyno].key_part[kp].store_length;
tab->loosescan_key_len = keylen;
if (pos->n_sj_tables > 1) {
last_sj_tab->firstmatch_return = tab->idx();
last_sj_tab->match_tab = last_sj_tab->idx();
}
tableno += pos->n_sj_tables;
break;
}
case SJ_OPT_DUPS_WEEDOUT: {
assert(tab_in_sj_nest); // First table must be inner
/*
Consider a semijoin of one outer and one inner table, both
with two rows. The inner table is assumed to be confluent
(See sj_opt_materialize_lookup)
If normal nested loop execution is used, we do not need to
include semi-join outer table rowids in the duplicate
weedout temp table since NL guarantees that outer table rows
are encountered only consecutively and because all rows in
the temp table are deleted for every new outer table
combination (example is with a confluent inner table):
ot1.row1|it1.row1
'-> temp table's have_confluent_row == false
|-> output ot1.row1
'-> set have_confluent_row= true
ot1.row1|it1.row2
|-> temp table's have_confluent_row == true
| '-> do not output ot1.row1
'-> no more join matches - set have_confluent_row= false
ot1.row2|it1.row1
'-> temp table's have_confluent_row == false
|-> output ot1.row2
'-> set have_confluent_row= true
...
Note: not having outer table rowids in the temp table and
then emptying the temp table when a new outer table row
combinition is encountered is an optimization. Including
outer table rowids in the temp table is not harmful but
wastes memory.
Now consider the join buffering algorithms (BNL/BKA). These
algorithms join each inner row with outer rows in "reverse"
order compared to NL. Effectively, this means that outer
table rows may be encountered multiple times in a
non-consecutive manner:
NL: BNL/BKA:
ot1.row1|it1.row1 ot1.row1|it1.row1
ot1.row1|it1.row2 ot1.row2|it1.row1
ot1.row2|it1.row1 ot1.row1|it1.row2
ot1.row2|it1.row2 ot1.row2|it1.row2
It is clear from the above that there is no place we can
empty the temp table like we do in NL to avoid storing outer
table rowids.
Below we check if join buffering might be used. If so, set
first_table to the first non-constant table so that outer
table rowids are included in the temp table. Do not destroy
other duplicate elimination methods.
*/
uint first_table = tableno;
for (uint sj_tableno = tableno; sj_tableno < tableno + pos->n_sj_tables;
sj_tableno++) {
if (join->best_ref[sj_tableno]->use_join_cache() &&
sj_tableno <= no_jbuf_after) {
/* Join buffering will probably be used */
first_table = join->const_tables;
break;
}
}
QEP_TAB *const first_sj_tab = qep_array + first_table;
if (last_sj_tab->first_inner() != NO_PLAN_IDX &&
first_sj_tab->first_inner() != last_sj_tab->first_inner()) {
/*
The first duplicate weedout table is an outer table of an outer join
and the last duplicate weedout table is one of the inner tables of
the outer join.
In this case, we must assure that all the inner tables of the
outer join are part of the duplicate weedout operation.
This is to assure that NULL-extension for inner tables of an
outer join is performed before duplicate elimination is performed,
otherwise we will have extra NULL-extended rows being output, which
should have been eliminated as duplicates.
*/
QEP_TAB *tab2 = &qep_array[last_sj_tab->first_inner()];
/*
First, locate the table that is the first inner table of the
outer join operation that first_sj_tab is outer for.
*/
while (tab2->first_upper() != NO_PLAN_IDX &&
tab2->first_upper() != first_sj_tab->first_inner())
tab2 = qep_array + tab2->first_upper();
// Then, extend the range with all inner tables of the join nest:
if (qep_array[tab2->first_inner()].last_inner() > last_sj_tab->idx())
last_sj_tab =
&qep_array[qep_array[tab2->first_inner()].last_inner()];
}
SJ_TMP_TABLE_TAB sjtabs[MAX_TABLES];
SJ_TMP_TABLE_TAB *last_tab = sjtabs;
/*
Walk through the range and remember
- tables that need their rowids to be put into temptable
- the last outer table
*/
for (QEP_TAB *tab_in_range = qep_array + first_table;
tab_in_range <= last_sj_tab; tab_in_range++) {
if (sj_table_is_included(join, join->best_ref[tab_in_range->idx()])) {
last_tab->qep_tab = tab_in_range;
++last_tab;
}
}
SJ_TMP_TABLE *sjtbl = create_sj_tmp_table(thd, join, sjtabs, last_tab);
if (sjtbl == nullptr) {
return true;
}
qep_array[first_table].flush_weedout_table = sjtbl;
last_sj_tab->check_weed_out_table = sjtbl;
tableno += pos->n_sj_tables;
break;
}
case SJ_OPT_FIRST_MATCH: {
/*
Setup a "jump" from the last table in the range of inner tables
to the last outer table before the inner tables.
*/
plan_idx jump_to = tab->idx() - 1;
assert(tab_in_sj_nest); // First table must be inner
for (QEP_TAB *tab_in_range = tab; tab_in_range <= last_sj_tab;
tab_in_range++) {
if (!join->best_ref[tab_in_range->idx()]->emb_sj_nest) {
/*
Let last non-correlated table be jump target for
subsequent inner tables.
*/
assert(false); // no "split jump" should exist.
jump_to = tab_in_range->idx();
} else {
/*
Assign jump target for last table in a consecutive range of
inner tables.
*/
if (tab_in_range == last_sj_tab ||
!join->best_ref[tab_in_range->idx() + 1]->emb_sj_nest) {
tab_in_range->firstmatch_return = jump_to;
tab_in_range->match_tab = last_sj_tab->idx();
}
}
}
tableno += pos->n_sj_tables;
break;
}
}
}
return false;
}
/*
Destroy all temporary tables created by NL-semijoin runtime
*/
static void destroy_sj_tmp_tables(JOIN *join) {
List_iterator<TABLE> it(join->sj_tmp_tables);
TABLE *table;
while ((table = it++)) {
/*
SJ-Materialization tables are initialized for either sequential reading
or index lookup, DuplicateWeedout tables are not initialized for read
(we only write to them), so need to call ha_index_or_rnd_end.
*/
if (table->file != nullptr) {
table->file->ha_index_or_rnd_end();
}
close_tmp_table(table);
free_tmp_table(table);
}
join->sj_tmp_tables.clear();
}
/**
Remove all rows from all temp tables used by NL-semijoin runtime
All rows must be removed from all temporary tables before every join
re-execution.
*/
bool JOIN::clear_sj_tmp_tables() {
List_iterator<TABLE> it(sj_tmp_tables);
TABLE *table;
while ((table = it++)) {
if (table->empty_result_table()) return true; /* purecov: inspected */
}
return false;
}
/// Empties all correlated materialized derived tables
bool JOIN::clear_corr_derived_tmp_tables() {
for (uint i = const_tables; i < tables; i++) {
auto tl = qep_tab[i].table_ref;
if (tl && tl->is_derived() && !tl->common_table_expr() &&
(tl->derived_query_expression()->uncacheable & UNCACHEABLE_DEPENDENT) &&
tl->table) {
/*
Applied only to non-CTE derived tables, as CTEs are reset in
Query_expression::clear_correlated_query_blocks()
*/
if (tl->derived_query_expression()->query_result()->reset()) return true;
}
}
return false;
}
/**
Reset the state of this join object so that it is ready for a
new execution.
*/
void JOIN::reset() {
DBUG_TRACE;
if (!executed) return;
// clang-format off
query_expression()->offset_limit_cnt = (ha_rows)(
query_block->offset_limit ? query_block->offset_limit->val_uint() : 0ULL);
// clang-format on
group_sent = false;
recursive_iteration_count = 0;
executed = false;
List_iterator<Window> li(query_block->m_windows);
Window *w;
while ((w = li++)) {
w->reset_round();
}
if (tmp_tables) {
for (uint tmp = primary_tables; tmp < primary_tables + tmp_tables; tmp++) {
(void)qep_tab[tmp].table()->empty_result_table();
}
}
clear_sj_tmp_tables();
set_ref_item_slice(REF_SLICE_SAVED_BASE);
if (qep_tab) {
if (query_block->derived_table_count) clear_corr_derived_tmp_tables();
/* need to reset ref access state (see EQRefIterator) */
for (uint i = 0; i < tables; i++) {
QEP_TAB *const tab = &qep_tab[i];
/*
If qep_tab==NULL, we may still have done ref access (to read a const
table); const tables will not be re-read in the next execution of this
subquery, so resetting key_err is not needed.
*/
tab->ref().key_err = true;
}
}
/* Reset of sum functions */
if (sum_funcs) {
Item_sum *func, **func_ptr = sum_funcs;
while ((func = *(func_ptr++))) func->clear();
}
if (query_block->has_ft_funcs()) {
/* TODO: move the code to JOIN::exec */
(void)init_ftfuncs(thd, query_block);
}
}
/**
Prepare join result.
@details Prepare join result prior to join execution or describing.
Instantiate derived tables and get schema tables result if necessary.
@return
true An error during derived or schema tables instantiation.
false Ok
*/
bool JOIN::prepare_result() {
DBUG_TRACE;
error = 0;
if (query_block->query_result()->start_execution(thd)) goto err;
return false;
err:
error = 1;
return true;
}
/**
Clean up and destroy join object.
*/
void JOIN::destroy() {
cond_equal = nullptr;
set_plan_state(NO_PLAN);
if (qep_tab) {
assert(!join_tab);
for (uint i = 0; i < tables; i++) {
TABLE *table = qep_tab[i].table();
if (table != nullptr) {
// These were owned by the root iterator, which we just destroyed.
// Keep filesort_free_buffers() from trying to call CleanupAfterQuery()
// on them.
table->sorting_iterator = nullptr;
table->duplicate_removal_iterator = nullptr;
}
qep_tab[i].cleanup();
}
} else if (thd->lex->using_hypergraph_optimizer()) {
// Same, for hypergraph queries.
for (Table_ref *tl = query_block->leaf_tables; tl; tl = tl->next_leaf) {
TABLE *table = tl->table;
if (table != nullptr) {
// For prepared statements, a derived table's temp table handler
// gets cleaned up at the end of prepare and it is setup again
// during optimization. However, if optimization for a derived
// table query block fails for some reason (E.g. Secondary engine
// rejects all the plans), handler is not setup for the rest of
// the derived tables. So we need to call set_keyread() only
// when handler is initialized.
// TODO(Chaithra): This should be moved to a more suitable place,
// perhaps TableRowIterator's destructor ?
if (table->file != nullptr) {
table->set_keyread(false);
}
table->sorting_iterator = nullptr;
table->duplicate_removal_iterator = nullptr;
}
}
for (JOIN::TemporaryTableToCleanup cleanup : temp_tables) {
if (cleanup.table != nullptr) {
cleanup.table->sorting_iterator = nullptr;
cleanup.table->duplicate_removal_iterator = nullptr;
}
close_tmp_table(cleanup.table);
free_tmp_table(cleanup.table);
::destroy_at(cleanup.temp_table_param);
}
for (Filesort *filesort : filesorts_to_cleanup) {
if (filesort != nullptr) ::destroy_at(filesort);
}
temp_tables.clear();
filesorts_to_cleanup.clear();
}
if (join_tab || best_ref) {
for (uint i = 0; i < tables; i++) {
JOIN_TAB *const tab = join_tab ? &join_tab[i] : best_ref[i];
tab->cleanup();
}
}
/*
We are not using tables anymore
Unlock all tables. We may be in an INSERT .... SELECT statement.
*/
// Run Cached_item DTORs!
group_fields.destroy_elements();
semijoin_deduplication_fields.destroy_elements();
tmp_table_param.cleanup();
/* Cleanup items referencing temporary table columns */
if (tmp_fields != nullptr) {
cleanup_item_list(tmp_fields[REF_SLICE_TMP1]);
cleanup_item_list(tmp_fields[REF_SLICE_TMP2]);
for (uint widx = 0; widx < m_windows.elements; widx++) {
cleanup_item_list(tmp_fields[REF_SLICE_WIN_1 + widx]);
}
}
destroy_sj_tmp_tables(this);
List_iterator<Semijoin_mat_exec> sjm_list_it(sjm_exec_list);
Semijoin_mat_exec *sjm;
while ((sjm = sjm_list_it++) != nullptr) ::destroy_at(sjm);
sjm_exec_list.clear();
keyuse_array.clear();
// Free memory for rollup arrays
if (query_block->olap == ROLLUP_TYPE) {
rollup_group_items.clear();
rollup_group_items.shrink_to_fit();
rollup_sums.clear();
rollup_sums.shrink_to_fit();
}
}
void JOIN::cleanup_item_list(const mem_root_deque<Item *> &items) const {
for (Item *item : items) {
item->cleanup();
}
}
/**
Optimize a query block and all inner query expressions
@param thd thread handler
@param finalize_access_paths
if true, finalize access paths, cf. FinalizePlanForQueryBlock
@returns false if success, true if error
*/
bool Query_block::optimize(THD *thd, bool finalize_access_paths) {
DBUG_TRACE;
assert(join == nullptr);
JOIN *const join_local = new (thd->mem_root) JOIN(thd, this);
if (!join_local) return true; /* purecov: inspected */
/*
Updating Query_block::join requires acquiring THD::LOCK_query_plan
to avoid races when EXPLAIN FOR CONNECTION is used.
*/
thd->lock_query_plan();
join = join_local;
thd->unlock_query_plan();
if (join->optimize(finalize_access_paths)) return true;
if (join->zero_result_cause && !is_implicitly_grouped()) return false;
for (Query_expression *query_expression = first_inner_query_expression();
query_expression;
query_expression = query_expression->next_query_expression()) {
// Derived tables and const subqueries are already optimized
if (!query_expression->is_optimized() &&
query_expression->optimize(thd, /*materialize_destination=*/nullptr,
/*create_iterators=*/false,
/*finalize_access_paths=*/true))
return true;
}
return false;
}
/**
Check privileges for all columns referenced from this query block.
Also check privileges for referenced subqueries.
@param thd thread handler
@returns false if success, true if error (insufficient privileges)
@todo - skip this if we have table SELECT privileges for all tables
*/
bool Query_block::check_column_privileges(THD *thd) {
const Column_privilege_tracker tracker(thd, SELECT_ACL);
for (Item *item : visible_fields()) {
if (item->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
}
if (m_current_table_nest &&
check_privileges_for_join(thd, m_current_table_nest))
return true;
if (where_cond() != nullptr &&
where_cond()->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
for (ORDER *group = group_list.first; group; group = group->next) {
if ((*group->item)
->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
}
if (having_cond() != nullptr &&
having_cond()->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
List_iterator<Window> wi(m_windows);
Window *w;
while ((w = wi++)) {
for (ORDER *wp = w->first_partition_by(); wp != nullptr; wp = wp->next)
if ((*wp->item)->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
for (ORDER *wo = w->first_order_by(); wo != nullptr; wo = wo->next)
if ((*wo->item)->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
}
for (ORDER *order = order_list.first; order; order = order->next) {
if ((*order->item)
->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
}
if (check_privileges_for_subqueries(thd)) return true;
return false;
}
/**
Check privileges for column references in a JOIN expression
@param thd thread handler
@param tables list of joined tables
@returns false if success, true if error (insufficient privileges)
*/
bool check_privileges_for_join(THD *thd, mem_root_deque<Table_ref *> *tables) {
thd->want_privilege = SELECT_ACL;
for (Table_ref *table_ref : *tables) {
if (table_ref->join_cond() != nullptr &&
table_ref->join_cond()->walk(&Item::check_column_privileges,
enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
if (table_ref->nested_join != nullptr &&
check_privileges_for_join(thd, &table_ref->nested_join->m_tables))
return true;
}
return false;
}
/**
Check privileges for column references in an item list
@param thd thread handler
@param items list of items
@param privileges the required privileges
@returns false if success, true if error (insufficient privileges)
*/
bool check_privileges_for_list(THD *thd, const mem_root_deque<Item *> &items,
Access_bitmask privileges) {
thd->want_privilege = privileges;
for (Item *item : items) {
if (item->walk(&Item::check_column_privileges, enum_walk::PREFIX,
pointer_cast<uchar *>(thd)))
return true;
}
return false;
}
/**
Check privileges for column references in subqueries of a query block
@param thd thread handler
@returns false if success, true if error (insufficient privileges)
*/
bool Query_block::check_privileges_for_subqueries(THD *thd) {
for (Query_expression *query_expression = first_inner_query_expression();
query_expression;
query_expression = query_expression->next_query_expression()) {
for (Query_block *sl = query_expression->first_query_block(); sl;
sl = sl->next_query_block()) {
if (sl->check_column_privileges(thd)) return true;
}
}
return false;
}
/*****************************************************************************
Go through all combinations of not marked tables and find the one
which uses least records
*****************************************************************************/
/**
Find how much space the previous read not const tables takes in cache.
*/
void calc_used_field_length(TABLE *table, bool needs_rowid,
uint *p_used_fieldlength) {
uint null_fields, blobs, fields, rec_length;
Field **f_ptr, *field;
uint uneven_bit_fields;
MY_BITMAP *read_set = table->read_set;
uneven_bit_fields = null_fields = blobs = fields = rec_length = 0;
for (f_ptr = table->field; (field = *f_ptr); f_ptr++) {
if (bitmap_is_set(read_set, field->field_index())) {
fields++;
rec_length += field->pack_length();
if (field->is_flag_set(BLOB_FLAG) || field->is_array()) blobs++;
if (!field->is_flag_set(NOT_NULL_FLAG)) null_fields++;
if (field->type() == MYSQL_TYPE_BIT && ((Field_bit *)field)->bit_len)
uneven_bit_fields++;
}
}
if (null_fields || uneven_bit_fields)
rec_length += (table->s->null_fields + 7) / 8;
if (table->is_nullable()) rec_length += sizeof(bool);
if (blobs) {
const uint blob_length = (uint)(table->file->stats.mean_rec_length -
(table->s->reclength - rec_length));
rec_length += max<uint>(4U, blob_length);
}
if (needs_rowid) {
rec_length += table->file->ref_length;
fields++;
}
*p_used_fieldlength = rec_length;
}
bool JOIN::init_ref_access() {
DBUG_TRACE;
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
for (uint tableno = const_tables; tableno < tables; tableno++) {
JOIN_TAB *const tab = best_ref[tableno];
if (tab->type() == JT_REF) // Here JT_REF means all kinds of ref access
{
assert(tab->position() && tab->position()->key);
if (create_ref_for_key(this, tab, tab->position()->key,
tab->prefix_tables()))
return true;
}
}
return false;
}
/**
Set the first_sj_inner_tab and last_sj_inner_tab fields for all tables
inside the semijoin nests of the query.
*/
void JOIN::set_semijoin_info() {
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
if (query_block->sj_nests.empty()) return;
for (uint tableno = const_tables; tableno < tables;) {
JOIN_TAB *const tab = best_ref[tableno];
const POSITION *const pos = tab->position();
if (!pos) {
tableno++;
continue;
}
switch (pos->sj_strategy) {
case SJ_OPT_NONE:
tableno++;
break;
case SJ_OPT_MATERIALIZE_LOOKUP:
case SJ_OPT_MATERIALIZE_SCAN:
case SJ_OPT_LOOSE_SCAN:
case SJ_OPT_DUPS_WEEDOUT:
case SJ_OPT_FIRST_MATCH:
/*
Remember the first and last semijoin inner tables; this serves to tell
a JOIN_TAB's semijoin strategy (like in setup_join_buffering()).
*/
const plan_idx last_sj_tab = tableno + pos->n_sj_tables - 1;
const plan_idx last_sj_inner = (pos->sj_strategy == SJ_OPT_DUPS_WEEDOUT)
?
/* Range may end with non-inner table
so cannot set last_sj_inner_tab */
NO_PLAN_IDX
: last_sj_tab;
for (plan_idx tab_in_range = tableno; tab_in_range <= last_sj_tab;
tab_in_range++) {
best_ref[tab_in_range]->set_first_sj_inner(tableno);
best_ref[tab_in_range]->set_last_sj_inner(last_sj_inner);
}
tableno += pos->n_sj_tables;
break;
}
}
}
void calc_length_and_keyparts(Key_use *keyuse, JOIN_TAB *tab, const uint key,
table_map used_tables, Key_use **chosen_keyuses,
uint *length_out, uint *keyparts_out,
table_map *dep_map, bool *maybe_null) {
assert(!dep_map || maybe_null);
uint keyparts = 0, length = 0;
uint found_part_ref_or_null = 0;
KEY *const keyinfo = tab->table()->key_info + key;
do {
/*
This Key_use is chosen if:
- it involves a key part at the right place (if index is (a,b) we
can have a search criterion on 'b' only if we also have a criterion
on 'a'),
- it references only tables earlier in the plan.
Moreover, the execution layer is limited to maximum one ref_or_null
keypart, as Index_lookup::null_ref_key is only one byte.
*/
if (!(~used_tables & keyuse->used_tables) && keyparts == keyuse->keypart &&
!(found_part_ref_or_null & keyuse->optimize)) {
assert(keyparts <= MAX_REF_PARTS);
if (chosen_keyuses) chosen_keyuses[keyparts] = keyuse;
keyparts++;
length += keyinfo->key_part[keyuse->keypart].store_length;
found_part_ref_or_null |= keyuse->optimize;
if (dep_map) {
*dep_map |= keyuse->val->used_tables();
*maybe_null |= keyinfo->key_part[keyuse->keypart].null_bit &&
(keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL);
}
}
keyuse++;
} while (keyuse->table_ref == tab->table_ref && keyuse->key == key);
if (keyparts <= 0) {
assert(false);
my_error(ER_INTERNAL_ERROR, MYF(0),
"Key not found"); // In debug build we assert, but in release we
// guard against a potential server exit with an
// error
return;
}
*length_out = length;
*keyparts_out = keyparts;
}
bool init_ref(THD *thd, unsigned keyparts, unsigned length, unsigned keyno,
Index_lookup *ref) {
ref->key_parts = keyparts;
ref->key_length = length;
ref->key = keyno;
if (!(ref->key_buff = thd->mem_root->ArrayAlloc<uchar>(ALIGN_SIZE(length))) ||
!(ref->key_buff2 =
thd->mem_root->ArrayAlloc<uchar>(ALIGN_SIZE(length))) ||
!(ref->key_copy = thd->mem_root->ArrayAlloc<store_key *>(keyparts)) ||
!(ref->items = thd->mem_root->ArrayAlloc<Item *>(keyparts)) ||
!(ref->cond_guards = thd->mem_root->ArrayAlloc<bool *>(keyparts))) {
return true;
}
ref->key_err = true;
ref->null_rejecting = 0;
ref->use_count = 0;
ref->disable_cache = false;
return false;
}
bool init_ref_part(THD *thd, unsigned part_no, Item *val, bool *cond_guard,
bool null_rejecting, table_map const_tables,
table_map used_tables, bool nullable,
const KEY_PART_INFO *key_part_info, uchar *key_buff,
Index_lookup *ref) {
ref->items[part_no] = val; // Save for cond removal
ref->cond_guards[part_no] = cond_guard;
// Set ref as "null rejecting" only if either side is really nullable:
if (null_rejecting && (nullable || val->is_nullable()))
ref->null_rejecting |= (key_part_map)1 << part_no;
store_key *s_key = get_store_key(thd, val, used_tables, const_tables,
key_part_info, key_buff, nullable);
if (unlikely(!s_key || thd->is_error())) return true;
if (used_tables & ~INNER_TABLE_BIT) {
/* Comparing against a non-constant. */
ref->key_copy[part_no] = s_key;
} else {
/*
The outer reference is to a const table, so we copy the value
straight from that table now (during optimization), instead of from
the temporary table created during execution.
TODO: Synchronize with the temporary table creation code, so that
there is no need to create a column for this value.
*/
bool dummy_value = false;
val->walk(&Item::repoint_const_outer_ref, enum_walk::PREFIX,
pointer_cast<uchar *>(&dummy_value));
/*
key is const, copy value now and possibly skip it while ::exec().
Note:
Result check of store_key::copy() is unnecessary,
it could be an error returned by store_key::copy() method
but stored value is not null and default value could be used
in this case. Methods which used for storing the value
should be responsible for proper null value setting
in case of an error. Thus it's enough to check s_key->null_key
value only.
*/
(void)s_key->copy();
/*
It should be reevaluated in ::exec() if
constant evaluated to NULL value which we might need to
handle as a special case during JOIN::exec()
(As in : 'Full scan on NULL key')
*/
if (s_key->null_key)
ref->key_copy[part_no] = s_key; // Reevaluate in JOIN::exec()
else
ref->key_copy[part_no] = nullptr;
}
return false;
}
/**
Setup a ref access for looking up rows via an index (a key).
@param join The join object being handled
@param j The join_tab which will have the ref access populated
@param org_keyuse First key part of (possibly multi-part) key
@param used_tables Bitmap of available tables
@return False if success, True if error
Given a Key_use structure that specifies the fields that can be used
for index access, this function creates and set up the structure
used for index look up via one of the access methods {JT_FT,
JT_CONST, JT_REF_OR_NULL, JT_REF, JT_EQ_REF} for the plan operator
'j'. Generally the function sets up the structure j->ref (of type
Index_lookup), and the access method j->type.
@note We cannot setup fields used for ref access before we have sorted
the items within multiple equalities according to the final order of
the tables involved in the join operation. Currently, this occurs in
@see substitute_for_best_equal_field().
The exception is ref access for const tables, which are fixed
before the greedy search planner is invoked.
*/
bool create_ref_for_key(JOIN *join, JOIN_TAB *j, Key_use *org_keyuse,
table_map used_tables) {
DBUG_TRACE;
const uint key = org_keyuse->key;
const bool ftkey = (org_keyuse->keypart == FT_KEYPART);
THD *const thd = join->thd;
uint keyparts, length;
TABLE *const table = j->table();
KEY *const keyinfo = table->key_info + key;
Key_use *chosen_keyuses[MAX_REF_PARTS];
assert(j->keys().is_set(org_keyuse->key));
/* Calculate the length of the used key. */
if (ftkey) {
Item_func_match *ifm = down_cast<Item_func_match *>(org_keyuse->val);
length = 0;
keyparts = 1;
ifm->get_master()->score_from_index_scan = true;
} else /* not ftkey */
calc_length_and_keyparts(org_keyuse, j, key, used_tables, chosen_keyuses,
&length, &keyparts, nullptr, nullptr);
if (thd->is_error()) {
return true;
}
/* set up fieldref */
if (init_ref(thd, keyparts, length, (int)key, &j->ref())) {
return true;
}
uchar *key_buff = j->ref().key_buff;
uchar *null_ref_key = nullptr;
bool keyuse_uses_no_tables = true;
bool null_rejecting_key = true;
if (ftkey) {
Key_use *keyuse = org_keyuse;
j->ref().items[0] = ((Item_func *)(keyuse->val))->key_item();
/* Predicates pushed down into subquery can't be used FT access */
j->ref().cond_guards[0] = nullptr;
// not supported yet. SerG
assert(!(keyuse->used_tables & ~PSEUDO_TABLE_BITS));
j->set_type(JT_FT);
j->set_ft_func(down_cast<Item_func_match *>(keyuse->val));
memset(j->ref().key_copy, 0, sizeof(j->ref().key_copy[0]) * keyparts);
return false;
}
// Set up Index_lookup based on chosen Key_use-s.
for (uint part_no = 0; part_no < keyparts; part_no++) {
Key_use *keyuse = chosen_keyuses[part_no];
const bool nullable = keyinfo->key_part[part_no].null_bit;
if (keyuse->val->type() == Item::FIELD_ITEM) {
// Look up the most appropriate field to base the ref access on.
keyuse->val = get_best_field(down_cast<Item_field *>(keyuse->val),
join->cond_equal);
keyuse->used_tables = keyuse->val->used_tables();
}
if (init_ref_part(thd, part_no, keyuse->val, keyuse->cond_guard,
keyuse->null_rejecting, join->const_table_map,
keyuse->used_tables, nullable,
&keyinfo->key_part[part_no], key_buff, &j->ref())) {
return true;
}
keyuse_uses_no_tables = keyuse_uses_no_tables && !keyuse->used_tables;
/*
Remember if we are going to use REF_OR_NULL
But only if field _really_ can be null i.e. we force JT_REF
instead of JT_REF_OR_NULL in case if field can't be null
*/
if ((keyuse->optimize & KEY_OPTIMIZE_REF_OR_NULL) && nullable) {
assert(null_ref_key == nullptr); // or we would overwrite it below
null_ref_key = key_buff;
}
/*
The selected key will reject matches on NULL values if:
- the key field is nullable, and
- predicate rejects NULL values (keyuse->null_rejecting is true), or
- JT_REF_OR_NULL is not effective.
*/
if ((keyinfo->key_part[part_no].field->is_nullable() ||
table->is_nullable()) &&
(!keyuse->null_rejecting || null_ref_key != nullptr)) {
null_rejecting_key = false;
}
key_buff += keyinfo->key_part[part_no].store_length;
}
assert(j->type() != JT_FT);
if (j->type() == JT_CONST)
j->table()->const_table = true;
else if (((actual_key_flags(keyinfo) & HA_NOSAME) == 0) ||
((actual_key_flags(keyinfo) & HA_NULL_PART_KEY) &&
!null_rejecting_key) ||
keyparts != actual_key_parts(keyinfo)) {
/* Must read with repeat */
j->set_type(null_ref_key ? JT_REF_OR_NULL : JT_REF);
j->ref().null_ref_key = null_ref_key;
} else if (keyuse_uses_no_tables &&
!(table->file->ha_table_flags() & HA_BLOCK_CONST_TABLE)) {
/*
This happen if we are using a constant expression in the ON part
of an LEFT JOIN.
SELECT * FROM a LEFT JOIN b ON b.key=30
Here we should not mark the table as a 'const' as a field may
have a 'normal' value or a NULL value.
*/
j->set_type(JT_CONST);
j->position()->rows_fetched = 1.0;
} else {
j->set_type(JT_EQ_REF);
j->position()->rows_fetched = 1.0;
}
return thd->is_error();
}
namespace {
class store_key_const_item final : public store_key {
int cached_result = -1;
public:
store_key_const_item(THD *thd, Field *to_field_arg, uchar *ptr,
uchar *null_ptr_arg, uint length, Item *item_arg)
: store_key(thd, to_field_arg, ptr, null_ptr_arg, length, item_arg) {}
const char *name() const override { return STORE_KEY_CONST_NAME; }
protected:
enum store_key_result copy_inner() override {
if (cached_result == -1) {
cached_result = store_key::copy_inner();
}
return static_cast<store_key_result>(cached_result);
}
};
/*
Class used for indexes over JSON expressions. The value to lookup is
obtained from val_json() method and then converted according to field's
result type and saved. This allows proper handling of temporal values.
*/
class store_key_json_item final : public store_key {
/// Whether the key is constant.
const bool m_const_key{false};
/// Whether the key was already copied.
bool m_inited{false};
public:
store_key_json_item(THD *thd, Field *to_field_arg, uchar *ptr,
uchar *null_ptr_arg, uint length, Item *item_arg,
bool const_key_arg)
: store_key(thd, to_field_arg, ptr, null_ptr_arg, length, item_arg),
m_const_key(const_key_arg) {}
const char *name() const override {
return m_const_key ? STORE_KEY_CONST_NAME : "func";
}
protected:
enum store_key_result copy_inner() override;
};
} // namespace
static store_key *get_store_key(THD *thd, Item *val, table_map used_tables,
table_map const_tables,
const KEY_PART_INFO *key_part, uchar *key_buff,
uint maybe_null) {
if (key_part->field->is_array()) {
return new (thd->mem_root)
store_key_json_item(thd, key_part->field, key_buff + maybe_null,
maybe_null ? key_buff : nullptr, key_part->length,
val, (!((~const_tables) & used_tables)));
}
if (!((~const_tables) & used_tables)) // if const item
{
return new (thd->mem_root) store_key_const_item(
thd, key_part->field, key_buff + maybe_null,
maybe_null ? key_buff : nullptr, key_part->length, val);
}
return new (thd->mem_root)
store_key(thd, key_part->field, key_buff + maybe_null,
maybe_null ? key_buff : nullptr, key_part->length, val);
}
store_key::store_key(THD *thd, Field *field_arg, uchar *ptr, uchar *null,
uint length, Item *item_arg)
: item(item_arg) {
if (field_arg->type() == MYSQL_TYPE_BLOB ||
field_arg->type() == MYSQL_TYPE_GEOMETRY) {
/*
Key segments are always packed with a 2 byte length prefix.
See mi_rkey for details.
*/
to_field = new (thd->mem_root) Field_varstring(
ptr, length, 2, null, 1, Field::NONE, field_arg->field_name,
field_arg->table->s, field_arg->charset());
to_field->init(field_arg->table);
} else
to_field =
field_arg->new_key_field(thd->mem_root, field_arg->table, ptr, null, 1);
// If the item is nullable, but we cannot store null, make
// to_field temporary nullable so that we can check in copy_inner()
// if we end up with an illegal null value.
if (!to_field->is_nullable() && item->is_nullable())
to_field->set_tmp_nullable();
}
store_key::store_key_result store_key::copy() {
enum store_key_result result;
THD *thd = current_thd;
const enum_check_fields saved_check_for_truncated_fields =
thd->check_for_truncated_fields;
const sql_mode_t sql_mode = thd->variables.sql_mode;
thd->variables.sql_mode &= ~(MODE_NO_ZERO_IN_DATE | MODE_NO_ZERO_DATE);
thd->check_for_truncated_fields = CHECK_FIELD_IGNORE;
result = copy_inner();
thd->check_for_truncated_fields = saved_check_for_truncated_fields;
thd->variables.sql_mode = sql_mode;
return result;
}
enum store_key::store_key_result store_key_hash_item::copy_inner() {
const enum store_key_result res = store_key::copy_inner();
if (res != STORE_KEY_FATAL) {
// Convert to and from little endian, since that is what gets
// stored in the hash field we are lookup up against.
ulonglong h = uint8korr(pointer_cast<char *>(hash));
h = calc_field_hash(to_field, &h);
int8store(pointer_cast<char *>(hash), h);
}
return res;
}
namespace {
enum store_key::store_key_result store_key_json_item::copy_inner() {
THD *thd = current_thd;
TABLE *table = to_field->table;
// Temporarily mark all table's fields writable to avoid assert.
my_bitmap_map *old_map = dbug_tmp_use_all_columns(table, table->write_set);
if (!m_inited) {
Json_wrapper wr;
String str_val, buf;
const Functional_index_error_handler functional_index_error_handler(
to_field, thd);
// Get JSON value and store its value as the key. MEMBER OF is the only
// function that can use this function
if (get_json_atom_wrapper(&item, 0, "MEMBER OF", &str_val, &buf, &wr,
nullptr, true) ||
save_json_to_field(thd, to_field, &wr, false))
return STORE_KEY_FATAL;
// Copy constant key only once
if (m_const_key) m_inited = true;
}
dbug_tmp_restore_column_map(table->write_set, old_map);
null_key = to_field->is_null() || item->null_value;
assert(!thd->is_error());
return STORE_KEY_OK;
}
} // namespace
static store_key::store_key_result type_conversion_status_to_store_key(
THD *thd, type_conversion_status ts) {
switch (ts) {
case TYPE_OK:
return store_key::STORE_KEY_OK;
case TYPE_NOTE_TRUNCATED:
case TYPE_WARN_TRUNCATED:
case TYPE_NOTE_TIME_TRUNCATED:
if (thd->check_for_truncated_fields)
return store_key::STORE_KEY_CONV;
else
return store_key::STORE_KEY_OK;
case TYPE_WARN_OUT_OF_RANGE:
case TYPE_WARN_INVALID_STRING:
case TYPE_ERR_NULL_CONSTRAINT_VIOLATION:
case TYPE_ERR_BAD_VALUE:
case TYPE_ERR_OOM:
return store_key::STORE_KEY_FATAL;
}
assert(false); // not possible
return store_key::STORE_KEY_FATAL;
}
enum store_key::store_key_result store_key::copy_inner() {
THD *thd = current_thd;
TABLE *table = to_field->table;
my_bitmap_map *old_map = dbug_tmp_use_all_columns(table, table->write_set);
const type_conversion_status save_res = item->save_in_field(to_field, true);
store_key_result res;
/*
Item::save_in_field() may call Item::val_xxx(). And if this is a subquery
we need to check for errors executing it and react accordingly.
*/
if (save_res != TYPE_OK && thd->is_error())
res = STORE_KEY_FATAL;
else
res = type_conversion_status_to_store_key(thd, save_res);
dbug_tmp_restore_column_map(table->write_set, old_map);
null_key = to_field->is_null() || item->null_value;
return to_field->is_tmp_null() ? STORE_KEY_FATAL : res;
}
/**
Extend e1 by AND'ing e2 to the condition e1 points to. The resulting
condition is fixed. Requirement: the input Items must already have
been fixed. This is a variant of and_items(); it is intended for use in
the optimizer phase.
@param[in,out] e1 Pointer to condition that will be extended with e2
@param e2 Condition that will extend e1
@retval true if there was a memory allocation error, in which case
e1 remains unchanged
@retval false otherwise
*/
bool and_conditions(Item **e1, Item *e2) {
assert(!(*e1) || (*e1)->fixed);
assert(!e2 || e2->fixed);
if (*e1) {
if (!e2) return false;
Item *res = new Item_cond_and(*e1, e2);
if (unlikely(!res)) return true;
*e1 = res;
res->quick_fix_field();
res->update_used_tables();
} else
*e1 = e2;
return false;
}
/*
Get a part of the condition that can be checked using only index fields
SYNOPSIS
make_cond_for_index()
cond The source condition
table The table that is partially available
keyno The index in the above table. Only fields covered by the
index are available other_tbls_ok true <=> Fields of other non-const tables
are allowed
DESCRIPTION
Get a part of the condition that can be checked when for the given table
we have values only of fields covered by some index. The condition may
refer to other tables, it is assumed that we have values of all of their
fields.
Example:
make_cond_for_index(
"cond(t1.field) AND cond(t2.key1) AND cond(t2.non_key) AND
cond(t2.key2)", t2, keyno(t2.key1)) will return "cond(t1.field) AND
cond(t2.key2)"
RETURN
Index condition, or NULL if no condition could be inferred.
*/
static Item *make_cond_for_index(Item *cond, TABLE *table, uint keyno,
bool other_tbls_ok) {
assert(cond != nullptr);
if (cond->type() == Item::COND_ITEM) {
uint n_marked = 0;
if (((Item_cond *)cond)->functype() == Item_func::COND_AND_FUNC) {
table_map used_tables = 0;
Item_cond_and *new_cond = new Item_cond_and;
if (!new_cond) return nullptr;
List_iterator<Item> li(*((Item_cond *)cond)->argument_list());
Item *item;
while ((item = li++)) {
Item *fix = make_cond_for_index(item, table, keyno, other_tbls_ok);
if (fix) {
new_cond->argument_list()->push_back(fix);
used_tables |= fix->used_tables();
}
n_marked += (item->marker == Item::MARKER_ICP_COND_USES_INDEX_ONLY);
}
if (n_marked == ((Item_cond *)cond)->argument_list()->elements)
cond->marker = Item::MARKER_ICP_COND_USES_INDEX_ONLY;
switch (new_cond->argument_list()->elements) {
case 0:
return nullptr;
case 1:
new_cond->set_used_tables(used_tables);
return new_cond->argument_list()->head();
default:
new_cond->quick_fix_field();
new_cond->set_used_tables(used_tables);
return new_cond;
}
} else /* It's OR */
{
Item_cond_or *new_cond = new Item_cond_or;
if (!new_cond) return nullptr;
List_iterator<Item> li(*((Item_cond *)cond)->argument_list());
Item *item;
while ((item = li++)) {
Item *fix = make_cond_for_index(item, table, keyno, other_tbls_ok);
if (!fix) return nullptr;
new_cond->argument_list()->push_back(fix);
n_marked += (item->marker == Item::MARKER_ICP_COND_USES_INDEX_ONLY);
}
if (n_marked == ((Item_cond *)cond)->argument_list()->elements)
cond->marker = Item::MARKER_ICP_COND_USES_INDEX_ONLY;
new_cond->quick_fix_field();
new_cond->set_used_tables(cond->used_tables());
new_cond->apply_is_true();
return new_cond;
}
}
if (!uses_index_fields_only(cond, table, keyno, other_tbls_ok)) {
/*
Reset marker since it might have the value
MARKER_ICP_COND_USES_INDEX_ONLY if this condition is part of the select
condition for multiple tables.
*/
cond->marker = Item::MARKER_NONE;
return nullptr;
}
cond->marker = Item::MARKER_ICP_COND_USES_INDEX_ONLY;
return cond;
}
static Item *make_cond_remainder(Item *cond, bool exclude_index) {
if (exclude_index && cond->marker == Item::MARKER_ICP_COND_USES_INDEX_ONLY)
return nullptr; /* Already checked */
if (cond->type() == Item::COND_ITEM) {
table_map tbl_map = 0;
if (((Item_cond *)cond)->functype() == Item_func::COND_AND_FUNC) {
/* Create new top level AND item */
Item_cond_and *new_cond = new Item_cond_and;
if (!new_cond) return (Item *)nullptr;
List_iterator<Item> li(*((Item_cond *)cond)->argument_list());
Item *item;
while ((item = li++)) {
Item *fix = make_cond_remainder(item, exclude_index);
if (fix) {
new_cond->argument_list()->push_back(fix);
tbl_map |= fix->used_tables();
}
}
switch (new_cond->argument_list()->elements) {
case 0:
return (Item *)nullptr;
case 1:
return new_cond->argument_list()->head();
default:
new_cond->quick_fix_field();
new_cond->set_used_tables(tbl_map);
return new_cond;
}
} else /* It's OR */
{
Item_cond_or *new_cond = new Item_cond_or;
if (!new_cond) return (Item *)nullptr;
List_iterator<Item> li(*((Item_cond *)cond)->argument_list());
Item *item;
while ((item = li++)) {
Item *fix = make_cond_remainder(item, false);
if (!fix) return (Item *)nullptr;
new_cond->argument_list()->push_back(fix);
tbl_map |= fix->used_tables();
}
new_cond->quick_fix_field();
new_cond->set_used_tables(tbl_map);
new_cond->apply_is_true();
return new_cond;
}
}
return cond;
}
/**
Try to extract and push the index condition down to table handler
@param join_tab join_tab for table
@param keyno Index for which extract and push the condition
@param trace_obj trace object where information is to be added
*/
void QEP_TAB::push_index_cond(const JOIN_TAB *join_tab, uint keyno,
Opt_trace_object *trace_obj) {
JOIN *const join_ = join();
DBUG_TRACE;
ASSERT_BEST_REF_IN_JOIN_ORDER(join_);
assert(join_tab == join_->best_ref[idx()]);
if (join_tab->reversed_access) // @todo: historical limitation, lift it!
return;
TABLE *const tbl = table();
// Disable ICP for Innodb intrinsic temp table because of performance
if (tbl->s->db_type() == innodb_hton && tbl->s->tmp_table != NO_TMP_TABLE &&
tbl->s->tmp_table != TRANSACTIONAL_TMP_TABLE)
return;
// TODO: Currently, index on virtual generated column doesn't support ICP
if (tbl->vfield && tbl->index_contains_some_virtual_gcol(keyno)) return;
/*
Fields of other non-const tables aren't allowed in following cases:
type is:
(JT_ALL | JT_INDEX_SCAN | JT_RANGE | JT_INDEX_MERGE)
and BNL is used.
and allowed otherwise.
*/
const bool other_tbls_ok =
!((type() == JT_ALL || type() == JT_INDEX_SCAN || type() == JT_RANGE ||
type() == JT_INDEX_MERGE) &&
join_tab->use_join_cache() == JOIN_CACHE::ALG_BNL);
/*
We will only attempt to push down an index condition when the
following criteria are true:
0. The table has a select condition
1. The storage engine supports ICP.
2. The index_condition_pushdown switch is on and
the use of ICP is not disabled by the NO_ICP hint.
3. The query is not a multi-table update or delete statement. The reason
for this requirement is that the same handler will be used
both for doing the select/join and the update. The pushed index
condition might then also be applied by the storage engine
when doing the update part and result in either not finding
the record to update or updating the wrong record.
4. The JOIN_TAB is not part of a subquery that has guarded conditions
that can be turned on or off during execution of a 'Full scan on NULL
key'.
@see Item_in_optimizer::val_int()
@see subselect_iterator_engine::exec()
@see Index_lookup::cond_guards
@see setup_join_buffering
5. The join type is not CONST or SYSTEM. The reason for excluding
these join types, is that these are optimized to only read the
record once from the storage engine and later re-use it. In a
join where a pushed index condition evaluates fields from
tables earlier in the join sequence, the pushed condition would
only be evaluated the first time the record value was needed.
6. The index is not a clustered index. The performance improvement
of pushing an index condition on a clustered key is much lower
than on a non-clustered key. This restriction should be
re-evaluated when WL#6061 is implemented.
7. The index on virtual generated columns is not supported for ICP.
*/
if (condition() &&
tbl->file->index_flags(keyno, 0, true) & HA_DO_INDEX_COND_PUSHDOWN &&
hint_key_state(join_->thd, table_ref, keyno, ICP_HINT_ENUM,
OPTIMIZER_SWITCH_INDEX_CONDITION_PUSHDOWN) &&
join_->thd->lex->sql_command != SQLCOM_UPDATE_MULTI &&
join_->thd->lex->sql_command != SQLCOM_DELETE_MULTI &&
!has_guarded_conds() && type() != JT_CONST && type() != JT_SYSTEM &&
!(keyno == tbl->s->primary_key &&
tbl->file->primary_key_is_clustered())) {
DBUG_EXECUTE("where", print_where(join_->thd, condition(), "full cond",
QT_ORDINARY););
Item *idx_cond =
make_cond_for_index(condition(), tbl, keyno, other_tbls_ok);
DBUG_EXECUTE("where",
print_where(join_->thd, idx_cond, "idx cond", QT_ORDINARY););
if (idx_cond) {
/*
Check that the condition to push actually contains fields from
the index. Without any fields from the index it is unlikely
that it will filter out any records since the conditions on
fields from other tables in most cases have already been
evaluated.
*/
idx_cond->update_used_tables();
if ((idx_cond->used_tables() & table_ref->map()) == 0) {
/*
The following assert is to check that we only skip pushing the
index condition for the following situations:
1. We actually are allowed to generate an index condition on another
table.
2. The index condition is a constant item.
3. The index condition contains an updatable user variable
(test this by checking that the RAND_TABLE_BIT is set).
*/
assert(other_tbls_ok || // 1
idx_cond->const_item() || // 2
idx_cond->is_non_deterministic()); // 3
return;
}
Item *idx_remainder_cond = nullptr;
/*
For BKA cache, we don't store the condition, because evaluation of the
condition would require additional operations before the evaluation.
*/
if (join_tab->use_join_cache() &&
/*
if cache is used then the value is true only
for BKA cache (see setup_join_buffering() func).
In this case other_tbls_ok is an equivalent of
cache->is_key_access().
*/
other_tbls_ok &&
(idx_cond->used_tables() &
~(table_ref->map() | join_->const_table_map))) {
idx_remainder_cond = idx_cond;
trace_obj->add("not_pushed_due_to_BKA", true);
} else {
idx_remainder_cond = tbl->file->idx_cond_push(keyno, idx_cond);
DBUG_EXECUTE("where",
print_where(join_->thd, tbl->file->pushed_idx_cond,
"icp cond", QT_ORDINARY););
}
/*
Disable eq_ref's "lookup cache" if we've pushed down an index
condition.
TODO: This check happens to work on current ICP implementations, but
there may exist a compliant implementation that will not work
correctly with it. Sort this out when we stabilize the condition
pushdown APIs.
*/
if (idx_remainder_cond != idx_cond) {
ref().disable_cache = true;
trace_obj->add("pushed_index_condition", idx_cond);
}
Item *row_cond = make_cond_remainder(condition(), true);
DBUG_EXECUTE("where", print_where(join_->thd, row_cond, "remainder cond",
QT_ORDINARY););
if (row_cond) {
and_conditions(&row_cond, idx_remainder_cond);
idx_remainder_cond = row_cond;
}
set_condition(idx_remainder_cond);
trace_obj->add("table_condition_attached", idx_remainder_cond);
}
}
}
/**
Setup the materialized table for a semi-join nest
@param tab join_tab for the materialized semi-join table
@param tableno table number of materialized table
@param inner_pos information about the first inner table of the subquery
@param sjm_pos information about the materialized semi-join table,
to be filled with data.
@details
Setup execution structures for one semi-join materialization nest:
- Create the materialization temporary table, including Table_ref
object.
- Create a list of Item_field objects per column in the temporary table.
- Create a keyuse array describing index lookups into the table
(for MaterializeLookup)
@return False if OK, True if error
*/
bool JOIN::setup_semijoin_materialized_table(JOIN_TAB *tab, uint tableno,
POSITION *inner_pos,
POSITION *sjm_pos) {
DBUG_TRACE;
Table_ref *const emb_sj_nest = inner_pos->table->emb_sj_nest;
Semijoin_mat_optimize *const sjm_opt = &emb_sj_nest->nested_join->sjm;
Semijoin_mat_exec *const sjm_exec = tab->sj_mat_exec();
const uint field_count = emb_sj_nest->nested_join->sj_inner_exprs.size();
assert(field_count > 0);
assert(inner_pos->sj_strategy == SJ_OPT_MATERIALIZE_LOOKUP ||
inner_pos->sj_strategy == SJ_OPT_MATERIALIZE_SCAN);
/*
Set up the table to write to, do as
Query_result_union::create_result_table does
*/
sjm_exec->table_param = Temp_table_param();
count_field_types(query_block, &sjm_exec->table_param,
emb_sj_nest->nested_join->sj_inner_exprs, false, true);
sjm_exec->table_param.bit_fields_as_long = true;
char buffer[NAME_LEN];
const size_t len = snprintf(buffer, sizeof(buffer) - 1, "<subquery%u>",
emb_sj_nest->nested_join->query_block_id);
char *name = (char *)thd->mem_root->Alloc(len + 1);
if (name == nullptr) return true; /* purecov: inspected */
memcpy(name, buffer, len);
name[len] = '\0';
TABLE *table;
if (!(table =
create_tmp_table(thd, &sjm_exec->table_param,
emb_sj_nest->nested_join->sj_inner_exprs, nullptr,
true /* distinct */, true /* save_sum_fields */,
thd->variables.option_bits | TMP_TABLE_ALL_COLUMNS,
HA_POS_ERROR /* rows_limit */, name)))
return true; /* purecov: inspected */
sjm_exec->table = table;
map2table[tableno] = tab;
table->file->ha_extra(HA_EXTRA_IGNORE_DUP_KEY);
sj_tmp_tables.push_back(table);
sjm_exec_list.push_back(sjm_exec);
/*
Hash_field is not applicable for MATERIALIZE_LOOKUP. If hash_field is
created for temporary table, semijoin_types_allow_materialization must
assure that MATERIALIZE_LOOKUP can't be chosen.
*/
assert((inner_pos->sj_strategy == SJ_OPT_MATERIALIZE_LOOKUP &&
!table->hash_field) ||
inner_pos->sj_strategy == SJ_OPT_MATERIALIZE_SCAN);
auto tl = new (thd->mem_root) Table_ref("", name, TL_IGNORE);
if (tl == nullptr) return true; /* purecov: inspected */
tl->table = table;
/*
If the SJ nest is inside an outer join nest, this tmp table belongs to
it. It's important for attachment of the semi-join ON condition with the
proper guards, to this table. If it's an AJ nest it's an outer join
nest too.
*/
if (emb_sj_nest->is_aj_nest())
tl->embedding = emb_sj_nest;
else
tl->embedding = emb_sj_nest->outer_join_nest();
/*
Above, we do not set tl->emb_sj_nest, neither first_sj_inner nor
last_sj_inner; it's because there's no use to say that this table is part
of the SJ nest; but it's necessary to say that it's part of any outer join
nest. The antijoin nest is an outer join nest, but from the POV of the
sj-tmp table it's only an outer join nest, so there is no need to set
emb_sj_nest even in this case.
*/
// Table is "nullable" if inner table of an outer_join
if (tl->is_inner_table_of_outer_join()) table->set_nullable();
tl->set_tableno(tableno);
table->pos_in_table_list = tl;
table->pos_in_table_list->query_block = query_block;
if (!(sjm_opt->mat_fields = (Item_field **)thd->mem_root->Alloc(
field_count * sizeof(Item_field **))))
return true;
for (uint fieldno = 0; fieldno < field_count; fieldno++) {
if (!(sjm_opt->mat_fields[fieldno] =
new Item_field(table->visible_field_ptr()[fieldno])))
return true;
}
tab->table_ref = tl;
tab->set_table(table);
tab->set_position(sjm_pos);
tab->worst_seeks = 1.0;
tab->set_records((ha_rows)emb_sj_nest->nested_join->sjm.expected_rowcount);
tab->found_records = tab->records();
tab->read_time = emb_sj_nest->nested_join->sjm.scan_cost.total_cost();
tab->init_join_cond_ref(tl);
table->keys_in_use_for_query.set_all();
sjm_pos->table = tab;
sjm_pos->sj_strategy = SJ_OPT_NONE;
sjm_pos->use_join_buffer = false;
/*
No need to recalculate filter_effect since there are no post-read
conditions for materialized tables.
*/
sjm_pos->filter_effect = 1.0;
/*
Key_use objects are required so that create_ref_for_key() can set up
a proper ref access for this table.
*/
Key_use_array *keyuse =
create_keyuse_for_table(thd, field_count, sjm_opt->mat_fields,
emb_sj_nest->nested_join->sj_outer_exprs);
if (!keyuse) return true;
const double fanout =
((uint)tab->idx() == const_tables)
? 1.0
: best_ref[tab->idx() - 1]->position()->prefix_rowcount;
if (!sjm_exec->is_scan) {
sjm_pos->key = keyuse->begin(); // MaterializeLookup will use the index
sjm_pos->read_cost =
emb_sj_nest->nested_join->sjm.lookup_cost.total_cost() * fanout;
tab->set_keyuse(keyuse->begin());
tab->keys().set_bit(0); // There is one index - use it always
tab->set_index(0);
sjm_pos->rows_fetched = 1.0;
tab->set_type(JT_REF);
} else {
sjm_pos->key = nullptr; // No index use for MaterializeScan
sjm_pos->read_cost = tab->read_time * fanout;
sjm_pos->rows_fetched = static_cast<double>(tab->records());
tab->set_type(JT_ALL);
}
sjm_pos->set_prefix_join_cost((tab - join_tab), cost_model());
return false;
}
/**
A helper function that sets the right op type for join cache (BNL/BKA).
*/
void QEP_TAB::init_join_cache(JOIN_TAB *join_tab) {
assert(idx() > 0);
ASSERT_BEST_REF_IN_JOIN_ORDER(join());
assert(join_tab == join()->best_ref[idx()]);
switch (join_tab->use_join_cache()) {
case JOIN_CACHE::ALG_BNL:
op_type = QEP_TAB::OT_BNL;
break;
case JOIN_CACHE::ALG_BKA:
op_type = QEP_TAB::OT_BKA;
break;
default:
assert(0);
}
}
/**
Plan refinement stage: do various setup things for the executor
@param join Join being processed
@param no_jbuf_after Don't use join buffering after table with this number.
@return false if successful, true if error (Out of memory)
@details
Plan refinement stage: do various set ups for the executioner
- setup join buffering use
- push index conditions
- increment relevant counters
- etc
*/
bool make_join_readinfo(JOIN *join, uint no_jbuf_after) {
const bool statistics = !join->thd->lex->is_explain();
const bool prep_for_pos = join->need_tmp_before_win ||
join->select_distinct ||
!join->group_list.empty() || !join->order.empty() ||
join->m_windows.elements > 0;
DBUG_TRACE;
ASSERT_BEST_REF_IN_JOIN_ORDER(join);
Opt_trace_context *const trace = &join->thd->opt_trace;
const Opt_trace_object wrapper(trace);
const Opt_trace_array trace_refine_plan(trace, "refine_plan");
if (setup_semijoin_dups_elimination(join, no_jbuf_after))
return true; /* purecov: inspected */
for (uint i = join->const_tables; i < join->tables; i++) {
QEP_TAB *const qep_tab = &join->qep_tab[i];
if (!qep_tab->position()) continue;
JOIN_TAB *const tab = join->best_ref[i];
TABLE *const table = qep_tab->table();
Table_ref *const table_ref = qep_tab->table_ref;
/*
Need to tell handlers that to play it safe, it should fetch all
columns of the primary key of the tables: this is because MySQL may
build row pointers for the rows, and for all columns of the primary key
the read set has not necessarily been set by the server code.
*/
if (prep_for_pos) table->prepare_for_position();
Opt_trace_object trace_refine_table(trace);
trace_refine_table.add_utf8_table(table_ref);
if (tab->use_join_cache() != JOIN_CACHE::ALG_NONE)
qep_tab->init_join_cache(tab);
switch (qep_tab->type()) {
case JT_EQ_REF:
case JT_REF_OR_NULL:
case JT_REF:
case JT_SYSTEM:
case JT_CONST:
if (table->covering_keys.is_set(qep_tab->ref().key) &&
!table->no_keyread)
table->set_keyread(true);
else
qep_tab->push_index_cond(tab, qep_tab->ref().key,
&trace_refine_table);
break;
case JT_ALL:
join->thd->set_status_no_index_used();
qep_tab->using_dynamic_range = (tab->use_quick == QS_DYNAMIC_RANGE);
[[fallthrough]];
case JT_INDEX_SCAN:
if (tab->position()->filter_effect != COND_FILTER_STALE_NO_CONST &&
!tab->sj_mat_exec()) {
/*
rows_w_const_cond is # of rows which will be read by the access
method, minus those which will not pass the constant condition;
that's how calculate_scan_cost() works. Such number is useful inside
the planner, but obscure to the reader of EXPLAIN; so we put the
real count of read rows into rows_fetched, and move the constant
condition's filter to filter_effect.
*/
const double rows_w_const_cond = qep_tab->position()->rows_fetched;
table_ref->fetch_number_of_rows();
tab->position()->rows_fetched =
static_cast<double>(table->file->stats.records);
if (tab->position()->filter_effect != COND_FILTER_STALE) {
// Constant condition moves to filter_effect:
if (tab->position()->rows_fetched == 0) // avoid division by zero
tab->position()->filter_effect = 0.0f;
else
tab->position()->filter_effect *= static_cast<float>(
rows_w_const_cond / tab->position()->rows_fetched);
}
}
if (qep_tab->using_dynamic_range) {
join->thd->set_status_no_good_index_used();
if (statistics) join->thd->inc_status_select_range_check();
} else {
if (statistics) {
if (i == join->const_tables)
join->thd->inc_status_select_scan();
else
join->thd->inc_status_select_full_join();
}
}
break;
case JT_RANGE:
case JT_INDEX_MERGE:
qep_tab->using_dynamic_range = (tab->use_quick == QS_DYNAMIC_RANGE);
if (statistics) {
if (i == join->const_tables)
join->thd->inc_status_select_range();
else
join->thd->inc_status_select_full_range_join();
}
if (!table->no_keyread && qep_tab->type() == JT_RANGE) {
if (table->covering_keys.is_set(used_index(qep_tab->range_scan()))) {
assert(used_index(qep_tab->range_scan()) != MAX_KEY);
table->set_keyread(true);
}
if (!table->key_read)
qep_tab->push_index_cond(tab, used_index(qep_tab->range_scan()),
&trace_refine_table);
}
if (tab->position()->filter_effect != COND_FILTER_STALE_NO_CONST) {
const double rows_w_const_cond = qep_tab->position()->rows_fetched;
qep_tab->position()->rows_fetched =
tab->range_scan()->num_output_rows();
if (tab->position()->filter_effect != COND_FILTER_STALE) {
// Constant condition moves to filter_effect:
if (tab->position()->rows_fetched == 0) // avoid division by zero
tab->position()->filter_effect = 0.0f;
else
tab->position()->filter_effect *= static_cast<float>(
rows_w_const_cond / tab->position()->rows_fetched);
}
}
break;
case JT_FT:
if (tab->join()->fts_index_access(tab)) {
table->set_keyread(true);
table->covering_keys.set_bit(tab->ft_func()->key);
}
break;
default:
DBUG_PRINT("error", ("Table type %d found",
qep_tab->type())); /* purecov: deadcode */
assert(0);
break; /* purecov: deadcode */
}
if (tab->position()->filter_effect <= COND_FILTER_STALE) {
/*
Cost and rows produced needs to be updated to match the logic
in test_if_skip_sort_order().
*/
bool need_cost_update =
join->primary_tables == 1 &&
tab->position()->filter_effect == COND_FILTER_STALE_NO_CONST &&
table->s->has_secondary_engine();
/*
Give a proper value for EXPLAIN.
For performance reasons, we do not recalculate the filter for
non-EXPLAIN queries; thus, EXPLAIN CONNECTION may show 100%
for a query.
Also calculate the proper value if max_join_size is in effect and there
is a limit, since it's needed in order to calculate how many rows to
read from the base table if rows are filtered before the limit is
applied.
*/
tab->position()->filter_effect =
(join->thd->lex->is_explain() || need_cost_update ||
(join->m_select_limit != HA_POS_ERROR &&
!Overlaps(join->thd->variables.option_bits, OPTION_BIG_SELECTS)))
? calculate_condition_filter(
tab,
(tab->ref().key != -1) ? tab->position()->key : nullptr,
tab->prefix_tables() & ~table_ref->map(),
tab->position()->rows_fetched, false, false,
trace_refine_table)
: COND_FILTER_ALLPASS;
/*
Update the cost/rows data accordingly for single table queries. Updating
Multi-table queries here can lead to inconsistencies.
*/
if (need_cost_update)
tab->position()->set_prefix_join_cost(tab->idx(), join->cost_model());
}
assert(!table_ref->is_recursive_reference() || qep_tab->type() == JT_ALL);
qep_tab->set_reversed_access(tab->reversed_access);
// Materialize derived tables prior to accessing them.
if (table_ref->is_table_function()) {
qep_tab->materialize_table = QEP_TAB::MATERIALIZE_TABLE_FUNCTION;
if (tab->dependent) qep_tab->rematerialize = true;
} else if (table_ref->uses_materialization()) {
qep_tab->materialize_table = QEP_TAB::MATERIALIZE_DERIVED;
}
if (qep_tab->sj_mat_exec())
qep_tab->materialize_table = QEP_TAB::MATERIALIZE_SEMIJOIN;
if (table_ref->is_derived() &&
table_ref->derived_query_expression()->m_lateral_deps) {
auto deps = table_ref->derived_query_expression()->m_lateral_deps;
plan_idx last = NO_PLAN_IDX;
for (JOIN_TAB **tab2 = join->map2table; deps; tab2++, deps >>= 1) {
if (deps & 1) last = std::max(last, (*tab2)->idx());
}
/*
We identified the last dependency of table_ref in the plan, and it's
the table whose reading must trigger rematerialization of table_ref.
*/
if (last != NO_PLAN_IDX) {
QEP_TAB &t = join->qep_tab[last];
t.lateral_derived_tables_depend_on_me |= TableBitmap(i);
trace_refine_table.add_utf8("rematerialized_for_each_row_of",
t.table()->alias);
}
}
}
return false;
}
void JOIN_TAB::set_table(TABLE *t) {
if (t != nullptr) t->reginfo.join_tab = this;
m_qs->set_table(t);
}
void JOIN_TAB::init_join_cond_ref(Table_ref *tl) {
m_join_cond_ref = tl->join_cond_optim_ref();
}
/**
Cleanup table of join operation.
*/
void JOIN_TAB::cleanup() {
// Delete parts specific of JOIN_TAB:
if (table()) table()->reginfo.join_tab = nullptr;
// Delete shared parts:
if (join()->qep_tab) {
// deletion will be done by QEP_TAB
} else
qs_cleanup();
}
void QEP_TAB::cleanup() {
// Delete parts specific of QEP_TAB:
if (filesort != nullptr) ::destroy_at(filesort);
filesort = nullptr;
TABLE *const t = table();
if (t != nullptr) {
t->reginfo.qep_tab = nullptr;
t->const_table = false; // Note: Also done in TABLE::init()
}
// Delete shared parts:
qs_cleanup();
// Order of qs_cleanup() and this, matters:
if (op_type == QEP_TAB::OT_MATERIALIZE ||
op_type == QEP_TAB::OT_AGGREGATE_THEN_MATERIALIZE ||
op_type == QEP_TAB::OT_AGGREGATE_INTO_TMP_TABLE ||
op_type == QEP_TAB::OT_WINDOWING_FUNCTION) {
if (t != nullptr) // Check tmp table is not yet freed.
{
close_tmp_table(t);
free_tmp_table(t);
}
::destroy_at(tmp_table_param);
tmp_table_param = nullptr;
}
if (table_ref != nullptr && table_ref->uses_materialization()) {
assert(t == table_ref->table);
t->merge_keys.clear_all();
t->quick_keys.clear_all();
t->covering_keys.clear_all();
t->possible_quick_keys.clear_all();
close_tmp_table(t);
}
}
void QEP_shared_owner::qs_cleanup() {
/* Skip non-existing derived tables/views result tables */
if (table() &&
(table()->s->tmp_table != INTERNAL_TMP_TABLE || table()->is_created())) {
table()->set_keyread(false);
table()->file->ha_index_or_rnd_end();
free_io_cache(table());
filesort_free_buffers(table(), true);
Table_ref *const table_ref = table()->pos_in_table_list;
if (table_ref) {
table_ref->derived_keys_ready = false;
table_ref->derived_key_list.clear();
}
}
if (range_scan() != nullptr) ::destroy_at(range_scan());
}
uint QEP_TAB::sjm_query_block_id() const {
assert(sj_is_materialize_strategy(get_sj_strategy()));
for (uint i = 0; i < join()->primary_tables; ++i) {
// Find the sj-mat tmp table whose sj nest contains us:
Semijoin_mat_exec *const sjm = join()->qep_tab[i].sj_mat_exec();
if (sjm && (uint)idx() >= sjm->inner_table_index &&
(uint)idx() < sjm->inner_table_index + sjm->table_count)
return sjm->sj_nest->nested_join->query_block_id;
}
assert(false);
return 0;
}
/**
Extend join_tab->cond by AND'ing add_cond to it
@param add_cond The condition to AND with the existing cond
for this JOIN_TAB
@retval true if there was a memory allocation error
@retval false otherwise
*/
bool QEP_shared_owner::and_with_condition(Item *add_cond) {
Item *tmp = condition();
if (and_conditions(&tmp, add_cond)) return true;
set_condition(tmp);
return false;
}
/**
Partially cleanup JOIN after it has executed: close index or rnd read
(table cursors), free quick selects.
This function is called in the end of execution of a JOIN, before the used
tables are unlocked and closed.
For a join that is resolved using a temporary table, the first sweep is
performed against actual tables and an intermediate result is inserted
into the temporary table.
The last sweep is performed against the temporary table. Therefore,
the base tables and associated buffers used to fill the temporary table
are no longer needed, and this function is called to free them.
For a join that is performed without a temporary table, this function
is called after all rows are sent, but before EOF packet is sent.
For a simple SELECT with no subqueries this function performs a full
cleanup of the JOIN and calls mysql_unlock_read_tables to free used base
tables.
If a JOIN is executed for a subquery or if it has a subquery, we can't
do the full cleanup and need to do a partial cleanup only.
- If a JOIN is not the top level join, we must not unlock the tables
because the outer select may not have been evaluated yet, and we
can't unlock only selected tables of a query.
- Additionally, if this JOIN corresponds to a correlated subquery, we
should not free quick selects and join buffers because they will be
needed for the next execution of the correlated subquery.
- However, if this is a JOIN for a [sub]select, which is not
a correlated subquery itself, but has subqueries, we can free it
fully and also free JOINs of all its subqueries. The exception
is a subquery in SELECT list, e.g:
@code
SELECT a, (select max(b) from t1) group by c
@endcode
This subquery will not be evaluated at first sweep and its value will
not be inserted into the temporary table. Instead, it's evaluated
when selecting from the temporary table. Therefore, it can't be freed
here even though it's not correlated.
@todo
Unlock tables even if the join isn't top level select in the tree
*/
void JOIN::join_free() {
Query_expression *tmp_query_expression;
Query_block *sl;
/*
Optimization: if not EXPLAIN and we are done with the JOIN,
free all tables.
*/
const bool full = (!query_block->uncacheable && !thd->lex->is_explain());
bool can_unlock = full;
DBUG_TRACE;
cleanup();
for (tmp_query_expression = query_block->first_inner_query_expression();
tmp_query_expression;
tmp_query_expression = tmp_query_expression->next_query_expression())
for (sl = tmp_query_expression->first_query_block(); sl;
sl = sl->next_query_block()) {
Item_subselect *subselect = sl->master_query_expression()->item;
const bool full_local = full && (!subselect || subselect->is_evaluated());
/*
If this join is evaluated, we can partially clean it up and clean up
all its underlying joins even if they are correlated, only query plan
is left in case a user will run EXPLAIN FOR CONNECTION.
If this join is not yet evaluated, we still must clean it up to
close its table cursors -- it may never get evaluated, as in case of
... HAVING FALSE OR a IN (SELECT ...))
but all table cursors must be closed before the unlock.
*/
sl->cleanup_all_joins();
/* Can't unlock if at least one JOIN is still needed */
can_unlock = can_unlock && full_local;
}
/*
We are not using tables anymore
Unlock all tables. We may be in an INSERT .... SELECT statement.
*/
if (can_unlock && lock && thd->lock && !thd->locked_tables_mode &&
!(query_block->active_options() & SELECT_NO_UNLOCK) &&
!query_block->subquery_in_having &&
(query_block == thd->lex->unit->query_term()->query_block())) {
/*
TODO: unlock tables even if the join isn't top level select in the
tree.
*/
mysql_unlock_read_tables(thd, lock); // Don't free join->lock
DEBUG_SYNC(thd, "after_join_free_unlock");
lock = nullptr;
}
}
static void cleanup_table(TABLE *table) {
if (table->is_created()) {
table->file->ha_index_or_rnd_end();
}
free_io_cache(table);
filesort_free_buffers(table, false);
}
/**
Free resources of given join.
@note
With subquery this function definitely will be called several times,
but even for simple query it can be called several times.
*/
void JOIN::cleanup() {
DBUG_TRACE;
assert(const_tables <= primary_tables && primary_tables <= tables);
if (qep_tab || join_tab || best_ref) {
for (uint i = 0; i < tables; i++) {
QEP_TAB *qtab;
TABLE *table;
if (qep_tab) {
assert(!join_tab);
qtab = &qep_tab[i];
table = qtab->table();
} else {
qtab = nullptr;
table = (join_tab ? &join_tab[i] : best_ref[i])->table();
}
if (!table) continue;
cleanup_table(table);
}
} else if (thd->lex->using_hypergraph_optimizer()) {
for (Table_ref *tl = query_block->leaf_tables; tl; tl = tl->next_leaf) {
cleanup_table(tl->table);
}
for (JOIN::TemporaryTableToCleanup cleanup : temp_tables) {
cleanup_table(cleanup.table);
}
}
}
/**
Filter out ORDER BY items that are equal to constants in WHERE condition
This function is a limited version of remove_const() for use
with non-JOIN statements (i.e. single-table UPDATE and DELETE).
@param order Linked list of ORDER BY arguments.
@param where Where condition.
@return pointer to new filtered ORDER list or NULL if whole list eliminated
@note
This function overwrites input order list.
*/
ORDER *simple_remove_const(ORDER *order, Item *where) {
if (order == nullptr || where == nullptr) return order;
ORDER *first = nullptr, *prev = nullptr;
for (; order; order = order->next) {
assert(!order->item[0]->has_aggregation()); // should never happen
if (!check_field_is_const(where, order->item[0])) {
if (first == nullptr) first = order;
if (prev != nullptr) prev->next = order;
prev = order;
}
}
if (prev != nullptr) prev->next = nullptr;
return first;
}
bool equality_determines_uniqueness(const Item_func_comparison *func,
const Item *v, const Item *c) {
/*
- The "c" argument must be a constant.
- The result type of both arguments must be the same.
However, since a temporal type is also classified as a string type,
we do not allow a temporal constant to be considered equal to a
variable character string.
- If both arguments are strings, the comparison operator must have the same
collation as the ordering operation applied to the variable expression.
*/
return c->const_for_execution() && v->result_type() == c->result_type() &&
(v->result_type() != STRING_RESULT ||
(!(is_string_type(v->data_type()) &&
is_temporal_type(c->data_type())) &&
func->compare_collation() == v->collation.collation));
}
bool equality_has_no_implicit_casts(const Item_func_comparison *func,
const Item *item1, const Item *item2) {
// See equality_determines_uniqueness() for the logic around strings
// and dates.
if (item1->result_type() != item2->result_type()) {
return false;
}
if (item1->result_type() == STRING_RESULT) {
if (is_temporal_type(item1->data_type()) !=
is_temporal_type(item2->data_type())) {
return false;
}
if (is_string_type(item1->data_type()) !=
is_string_type(item2->data_type())) {
return false;
}
if (is_string_type(item1->data_type())) {
if (func->compare_collation() != item1->collation.collation ||
func->compare_collation() != item2->collation.collation) {
return false;
}
}
}
return true;
}
/*
Return true if i1 and i2 (if any) are equal items,
or if i1 is a wrapper item around the f2 field.
*/
static bool equal(const Item *i1, const Item *i2, const Field *f2) {
assert((i2 == nullptr) ^ (f2 == nullptr));
if (i2 != nullptr)
return i1->eq(i2, true);
else if (i1->type() == Item::FIELD_ITEM)
return f2->eq(down_cast<const Item_field *>(i1)->field);
else
return false;
}
/**
Check if a field is equal to a constant value in a condition
@param cond condition to search within
@param order_item Item to find in condition (if order_field is NULL)
@param order_field Field to find in condition (if order_item is NULL)
@param[out] const_item Used in calculation with conjunctive predicates,
must be NULL in outer-most call.
@returns true if the field is a constant value in condition, false otherwise
*/
bool check_field_is_const(Item *cond, const Item *order_item,
const Field *order_field, Item **const_item) {
assert((order_item == nullptr) ^ (order_field == nullptr));
Item *intermediate = nullptr;
if (const_item == nullptr) const_item = &intermediate;
if (cond->type() == Item::COND_ITEM) {
Item_cond *const c = down_cast<Item_cond *>(cond);
bool and_level = c->functype() == Item_func::COND_AND_FUNC;
List_iterator_fast<Item> li(*c->argument_list());
Item *item;
while ((item = li++)) {
if (check_field_is_const(item, order_item, order_field, const_item)) {
if (and_level) return true;
} else if (!and_level)
return false;
}
return !and_level;
}
if (cond->type() != Item::FUNC_ITEM) return false;
Item_func *const func = down_cast<Item_func *>(cond);
if (func->functype() != Item_func::EQUAL_FUNC &&
func->functype() != Item_func::EQ_FUNC)
return false;
Item_func_comparison *comp = down_cast<Item_func_comparison *>(func);
Item *left = comp->arguments()[0];
Item *right = comp->arguments()[1];
if (equal(left, order_item, order_field)) {
if (equality_determines_uniqueness(comp, left, right)) {
if (*const_item != nullptr) return right->eq(*const_item, true);
*const_item = right;
return true;
}
} else if (equal(right, order_item, order_field)) {
if (equality_determines_uniqueness(comp, right, left)) {
if (*const_item != nullptr) return left->eq(*const_item, true);
*const_item = left;
return true;
}
}
return false;
}
/**
Update TMP_TABLE_PARAM with count of the different type of fields.
This function counts the number of fields, functions and sum
functions (items with type SUM_FUNC_ITEM) for use by
create_tmp_table() and stores it in the Temp_table_param object. It
also updates the allow_group_via_temp_table property if needed.
@param query_block Query_block of query
@param param Description of temp table
@param fields List of fields to count
@param reset_with_sum_func Whether to reset with_sum_func of func items
@param save_sum_fields Count in the way create_tmp_table() expects when
given the same parameter.
*/
void count_field_types(const Query_block *query_block, Temp_table_param *param,
const mem_root_deque<Item *> &fields,
bool reset_with_sum_func, bool save_sum_fields) {
DBUG_TRACE;
param->sum_func_count = 0;
param->func_count = fields.size();
param->hidden_field_count = 0;
param->outer_sum_func_count = 0;
/*
Loose index scan guarantees that all grouping is done and MIN/MAX
functions are computed, so create_tmp_table() treats this as if
save_sum_fields is set.
*/
save_sum_fields |= param->precomputed_group_by;
for (Item *field : fields) {
Item *real = field->real_item();
Item::Type real_type = real->type();
if (real_type == Item::SUM_FUNC_ITEM && !real->m_is_window_function) {
if (!field->const_item()) {
Item_sum *sum_item = down_cast<Item_sum *>(field->real_item());
if (sum_item->aggr_query_block == query_block) {
if (!sum_item->allow_group_via_temp_table)
param->allow_group_via_temp_table = false; // UDF SUM function
param->sum_func_count++;
// Add one column per argument.
param->func_count += sum_item->argument_count();
}
} else if (save_sum_fields) {
/*
Count the way create_tmp_table() does if asked to preserve
Item_sum_* functions in fields list.
Item field is an Item_sum_* or a reference to such an
item. We need to distinguish between these two cases since
they are treated differently by create_tmp_table().
*/
if (field->type() != Item::SUM_FUNC_ITEM) {
// A reference to an Item_sum_*
param->func_count++; // TODO: Is this really needed?
param->sum_func_count++;
}
}
} else if (real_type == Item::SUM_FUNC_ITEM) {
assert(real->m_is_window_function);
Item_sum *window_item = down_cast<Item_sum *>(real);
param->func_count += window_item->argument_count();
} else {
if (reset_with_sum_func) field->reset_aggregation();
if (field->has_aggregation()) param->outer_sum_func_count++;
}
}
}
/**
Return 1 if second is a subpart of first argument.
If first parts has different direction, change it to second part
(group is sorted like order)
*/
bool test_if_subpart(ORDER *a, ORDER *b) {
ORDER *first = a;
ORDER *second = b;
for (; first && second; first = first->next, second = second->next) {
if ((*first->item)->eq(*second->item, true))
continue;
else
return false;
}
// If the second argument is not subpart of the first return false
if (second) return false;
// Else assign the direction of the second argument to the first
for (; a && b; a = a->next, b = b->next) a->direction = b->direction;
return true;
}
/**
calc how big buffer we need for comparing group entries.
*/
void calc_group_buffer(JOIN *join, ORDER *group) {
DBUG_TRACE;
uint key_length = 0, parts = 0, null_parts = 0;
if (group) join->grouped = true;
for (; group; group = group->next) {
Item *group_item = *group->item;
Field *field = group_item->get_tmp_table_field();
if (field) {
enum_field_types type;
if ((type = field->type()) == MYSQL_TYPE_BLOB)
key_length += MAX_BLOB_WIDTH; // Can't be used as a key
else if (type == MYSQL_TYPE_VARCHAR || type == MYSQL_TYPE_VAR_STRING)
key_length += field->field_length + HA_KEY_BLOB_LENGTH;
else if (type == MYSQL_TYPE_BIT) {
/* Bit is usually stored as a longlong key for group fields */
key_length += 8; // Big enough
} else
key_length += field->pack_length();
} else {
switch (group_item->result_type()) {
case REAL_RESULT:
key_length += sizeof(double);
break;
case INT_RESULT:
key_length += sizeof(longlong);
break;
case DECIMAL_RESULT:
key_length += my_decimal_get_binary_size(
group_item->max_length - (group_item->decimals ? 1 : 0),
group_item->decimals);
break;
case STRING_RESULT: {
/*
As items represented as DATE/TIME fields in the group buffer
have STRING_RESULT result type, we increase the length
by 8 as maximum pack length of such fields.
*/
if (group_item->is_temporal()) {
key_length += 8;
} else if (group_item->data_type() == MYSQL_TYPE_BLOB)
key_length += MAX_BLOB_WIDTH; // Can't be used as a key
else {
/*
Group strings are taken as varstrings and require an length field.
A field is not yet created by create_tmp_field()
and the sizes should match up.
*/
key_length += group_item->max_length + HA_KEY_BLOB_LENGTH;
}
break;
}
default:
/* This case should never be chosen */
assert(0);
my_error(ER_OUT_OF_RESOURCES, MYF(ME_FATALERROR));
}
}
parts++;
if (group_item->is_nullable()) null_parts++;
}
join->tmp_table_param.group_length = key_length + null_parts;
join->tmp_table_param.group_parts = parts;
join->tmp_table_param.group_null_parts = null_parts;
}
/**
Make an array of pointers to sum_functions to speed up
sum_func calculation.
@retval
0 ok
@retval
1 Error
*/
bool JOIN::alloc_func_list() {
uint func_count, group_parts;
DBUG_TRACE;
func_count = tmp_table_param.sum_func_count;
/*
If we are using rollup, we need a copy of the summary functions for
each level
*/
if (rollup_state != RollupState::NONE) func_count *= (send_group_parts + 1);
group_parts = send_group_parts;
/*
If distinct, reserve memory for possible
disctinct->group_by optimization
*/
if (select_distinct) {
group_parts += CountVisibleFields(*fields);
/*
If the ORDER clause is specified then it's possible that
it also will be optimized, so reserve space for it too
*/
if (!order.empty()) {
ORDER *ord;
for (ord = order.order; ord; ord = ord->next) group_parts++;
}
}
/* This must use calloc() as rollup_make_fields depends on this */
sum_funcs =
(Item_sum **)thd->mem_calloc(sizeof(Item_sum **) * (func_count + 1) +
sizeof(Item_sum ***) * (group_parts + 1));
return sum_funcs == nullptr;
}
/**
Initialize 'sum_funcs' array with all Item_sum objects.
@param fields All items
@param before_group_by Set to 1 if this is called before GROUP BY handling
@param recompute Set to true if sum_funcs must be recomputed
@retval
0 ok
@retval
1 error
*/
bool JOIN::make_sum_func_list(const mem_root_deque<Item *> &fields,
bool before_group_by, bool recompute) {
DBUG_TRACE;
if (*sum_funcs && !recompute)
return false; /* We have already initialized sum_funcs. */
Item_sum **func = sum_funcs;
for (Item *item : fields) {
if (item->type() == Item::SUM_FUNC_ITEM && !item->const_item() &&
down_cast<Item_sum *>(item)->aggr_query_block == query_block) {
assert(!item->m_is_window_function);
*func++ = down_cast<Item_sum *>(item);
}
}
if (before_group_by && rollup_state == RollupState::INITED) {
rollup_state = RollupState::READY;
} else if (rollup_state == RollupState::READY)
return false; // Don't put end marker
*func = nullptr; // End marker
return false;
}
/**
Free joins of subselect of this select.
@param select pointer to Query_block which subselects joins we will free
@todo when the final use of this function (from SET statements) is removed,
this function can be deleted.
*/
void free_underlaid_joins(Query_block *select) {
for (Query_expression *query_expression =
select->first_inner_query_expression();
query_expression;
query_expression = query_expression->next_query_expression())
query_expression->cleanup(false);
}
/**
Change the Query_result object of the query block.
If old_result is not used, forward the call to the current
Query_result in case it is a wrapper around old_result.
Call prepare() on the new Query_result if we decide to use it.
@param thd Thread handle
@param new_result New Query_result object
@param old_result Old Query_result object (NULL to force change)
@retval false Success
@retval true Error
*/
bool Query_block::change_query_result(THD *thd,
Query_result_interceptor *new_result,
Query_result_interceptor *old_result) {
DBUG_TRACE;
if (old_result == nullptr || query_result() == old_result) {
set_query_result(new_result);
if (query_result()->prepare(thd, fields, master_query_expression()))
return true; /* purecov: inspected */
return false;
} else {
const bool ret = query_result()->change_query_result(thd, new_result);
return ret;
}
}
/**
Add having condition as a filter condition, which is applied when reading
from the temp table.
@param curr_tmp_table Table number to which having conds are added.
@returns false if success, true if error.
*/
bool JOIN::add_having_as_tmp_table_cond(uint curr_tmp_table) {
having_cond->update_used_tables();
QEP_TAB *const curr_table = &qep_tab[curr_tmp_table];
table_map used_tables;
Opt_trace_context *const trace = &thd->opt_trace;
DBUG_TRACE;
if (curr_table->table_ref)
used_tables = curr_table->table_ref->map();
else {
/*
Pushing parts of HAVING to an internal temporary table.
Fields in HAVING condition may have been replaced with fields in an
internal temporary table. This table has map=1.
*/
assert(having_cond->has_subquery() ||
!(having_cond->used_tables() & ~(1 | PSEUDO_TABLE_BITS)));
used_tables = 1;
}
// Condition may contain outer references, const and non-deterministic exprs:
used_tables |= PSEUDO_TABLE_BITS;
/*
All conditions which can be applied after reading from used_tables are
added as filter conditions of curr_tmp_table. If condition's used_tables is
not read yet for example subquery in having, then it will be kept as it is
in original having_cond of join.
If ROLLUP, having condition needs to be tested after writing rollup data.
So do not move the having condition.
*/
Item *sort_table_cond =
(rollup_state == RollupState::NONE)
? make_cond_for_table(thd, having_cond, used_tables, table_map{0},
false)
: nullptr;
if (sort_table_cond) {
if (!curr_table->condition())
curr_table->set_condition(sort_table_cond);
else {
curr_table->set_condition(
new Item_cond_and(curr_table->condition(), sort_table_cond));
if (curr_table->condition()->fix_fields(thd, nullptr)) return true;
}
curr_table->condition()->apply_is_true();
DBUG_EXECUTE("where", print_where(thd, curr_table->condition(),
"select and having", QT_ORDINARY););
having_cond = make_cond_for_table(thd, having_cond, ~table_map{0},
~used_tables, false);
DBUG_EXECUTE("where", print_where(thd, having_cond, "having after sort",
QT_ORDINARY););
const Opt_trace_object trace_wrapper(trace);
Opt_trace_object(trace, "sort_using_internal_table")
.add("condition_for_sort", sort_table_cond)
.add("having_after_sort", having_cond);
}
return false;
}
bool CreateFramebufferTable(
THD *thd, const Temp_table_param &tmp_table_param,
const Query_block &query_block, const mem_root_deque<Item *> &source_fields,
const mem_root_deque<Item *> &window_output_fields,
Func_ptr_array *mapping_from_source_to_window_output, Window *window) {
/*
Create the window frame buffer tmp table. We create a
temporary table with same contents as the output tmp table
in the windowing pipeline (columns defined by
curr_all_fields), but used for intermediate storage, saving
the window's frame buffer now that we know the window needs
buffering.
*/
Temp_table_param *par =
new (thd->mem_root) Temp_table_param(thd->mem_root, tmp_table_param);
par->m_window_frame_buffer = true;
// Don't include temporary fields that originally came from
// a window function (or an expression containing a window function).
// Window functions are not relevant to store in the framebuffer,
// and in fact, trying to restore them would often overwrite
// good data we shouldn't.
//
// Not that the regular filtering in create_tmp_table() cannot do this
// for us, as it only sees the Item_field, not where it came from.
mem_root_deque<Item *> fb_fields(window_output_fields);
for (size_t i = 0; i < fb_fields.size(); ++i) {
Item *orig_item = source_fields[i];
if (orig_item->has_wf()) {
fb_fields[i] = nullptr;
}
}
fb_fields.erase(std::remove(fb_fields.begin(), fb_fields.end(), nullptr),
fb_fields.end());
count_field_types(&query_block, par, fb_fields, false, false);
TABLE *table =
create_tmp_table(thd, par, fb_fields, nullptr, false, false,
query_block.active_options(), HA_POS_ERROR, "");
if (table == nullptr) return true;
window->set_frame_buffer_param(par);
window->set_frame_buffer(table);
// For window function expressions we are to evaluate after
// framebuffering, we need to replace their arguments to point to the
// output table instead of the input table (we could probably also have
// used the framebuffer if we wanted). E.g., if our input is t1 and our
// output is <temporary>, we need to rewrite 1 + SUM(t1.x) OVER w into
// 1 + SUM(<temporary>.x) OVER w.
for (Func_ptr &ptr : *mapping_from_source_to_window_output) {
if (ptr.func()->has_wf()) {
ReplaceMaterializedItems(thd, ptr.func(),
*mapping_from_source_to_window_output,
/*need_exact_match=*/false);
}
}
return false;
}
/**
Init tmp tables usage info.
@details
This function finalizes execution plan by taking following actions:
.) tmp tables are created, but not instantiated (this is done during
execution). QEP_TABs dedicated to tmp tables are filled appropriately.
see JOIN::create_intermediate_table.
.) prepare fields lists (fields, all_fields, ref_item_array slices) for
each required stage of execution. These fields lists are set for
tmp tables' tabs and for the tab of last table in the join.
.) fill info for sorting/grouping/dups removal is prepared and saved to
appropriate tabs. Here is an example:
SELECT * from t1,t2 WHERE ... GROUP BY t1.f1 ORDER BY t2.f2, t1.f2
and lets assume that the table order in the plan is t1,t2.
In this case optimizer will sort for group only the first table as the
second one isn't mentioned in GROUP BY. The result will be materialized
in tmp table. As filesort can't sort join optimizer will sort tmp table
also. The first sorting (for group) is called simple as is doesn't
require tmp table. The Filesort object for it is created here - in
JOIN::create_intermediate_table. Filesort for the second case is
created here, in JOIN::make_tmp_tables_info.
@note
This function may change tmp_table_param.precomputed_group_by. This
affects how create_tmp_table() treats aggregation functions, so
count_field_types() must be called again to make sure this is taken
into consideration.
@returns
false - Ok
true - Error
*/
bool JOIN::make_tmp_tables_info() {
assert(!join_tab);
mem_root_deque<Item *> *curr_fields = fields;
bool materialize_join = false;
uint curr_tmp_table = const_tables;
TABLE *exec_tmp_table = nullptr;
auto cleanup_tmp_tables_on_error =
create_scope_guard([this, &curr_tmp_table] {
if (qep_tab == nullptr) {
return;
}
for (unsigned table_idx = primary_tables; table_idx <= curr_tmp_table;
++table_idx) {
TABLE *table = qep_tab[table_idx].table();
if (table != nullptr) {
close_tmp_table(table);
free_tmp_table(table);
qep_tab[table_idx].set_table(nullptr);
}
}
});
/*
If the plan is constant, we will not do window tmp table processing
cf. special code path for handling const plans.
*/
m_windowing_steps = m_windows.elements > 0 && !plan_is_const() &&
!implicit_grouping && !group_optimized_away;
const bool may_trace = // just to avoid an empty trace block
need_tmp_before_win || implicit_grouping || m_windowing_steps ||
!group_list.empty() || !order.empty();
Opt_trace_context *const trace = &thd->opt_trace;
const Opt_trace_disable_I_S trace_disabled(trace, !may_trace);
const Opt_trace_object wrapper(trace);
const Opt_trace_array trace_tmp(trace, "considering_tmp_tables");
DBUG_TRACE;
/*
In this function, we may change having_cond into a condition on a
temporary sort/group table, so we have to assign having_for_explain now:
*/
having_for_explain = having_cond;
const bool has_group_by = this->grouped;
/*
The loose index scan access method guarantees that all grouping or
duplicate row elimination (for distinct) is already performed
during data retrieval, and that all MIN/MAX functions are already
computed for each group. Thus all MIN/MAX functions should be
treated as regular functions, and there is no need to perform
grouping in the main execution loop.
Currently loose index scan is only applicable for single table queries. The
only exception is when a single table query becomes a multi-table query
because of a semijoin transformation. We check the first join_tab element
of the plan for its access method here, which holds good even for the
multi-table query, but only when optimizer has picked nested loop joins.
Skip scan is enabled only for the original table in the query which is the
first table in the join order for a nested loop join. However, for hash
joins it does not hold good. So, we see an additional de-duplication step
when hash join is picked as it is not aware that de-duplication is taken
care by the access method picked.
TODO: Make optimize_distinct_group_order() understand that de-duplication
is taken care by the chosen access method, so that we avoid the additional
de-duplication step.
*/
if (qep_tab && qep_tab[0].range_scan() &&
is_loose_index_scan(qep_tab[0].range_scan()))
tmp_table_param.precomputed_group_by =
!is_agg_loose_index_scan(qep_tab[0].range_scan());
/*
Create the first temporary table if distinct elimination is requested or
if the sort is too complicated to be evaluated as a filesort.
*/
if (need_tmp_before_win) {
curr_tmp_table = primary_tables;
Opt_trace_object trace_this_outer(trace);
trace_this_outer.add("adding_tmp_table_in_plan_at_position",
curr_tmp_table);
tmp_tables++;
/*
Make a copy of the base slice in the save slice.
This is needed because later steps will overwrite the base slice with
another slice (1-3).
After this slice has been used, overwrite the base slice again with
the copy in the save slice.
*/
if (alloc_ref_item_slice(thd, REF_SLICE_SAVED_BASE)) return true;
copy_ref_item_slice(REF_SLICE_SAVED_BASE, REF_SLICE_ACTIVE);
current_ref_item_slice = REF_SLICE_SAVED_BASE;
/*
Create temporary table for use in a single execution.
(Will be reused if this is a subquery that is executed several times
for one execution of the statement)
Don't use tmp table grouping for json aggregate funcs as it's
very ineffective.
*/
ORDER_with_src tmp_group;
if (!simple_group && !(test_flags & TEST_NO_KEY_GROUP) && !with_json_agg)
tmp_group = group_list;
tmp_table_param.hidden_field_count = CountHiddenFields(*fields);
if (create_intermediate_table(&qep_tab[curr_tmp_table], *fields, tmp_group,
!group_list.empty() && simple_group))
return true;
exec_tmp_table = qep_tab[curr_tmp_table].table();
if (exec_tmp_table->s->is_distinct) optimize_distinct();
/*
If there is no sorting or grouping, 'use_order'
index result should not have been requested.
Exception: LooseScan strategy for semijoin requires
sorted access even if final result is not to be sorted.
*/
assert(
!(m_ordered_index_usage == ORDERED_INDEX_VOID && !plan_is_const() &&
qep_tab[const_tables].position()->sj_strategy != SJ_OPT_LOOSE_SCAN &&
qep_tab[const_tables].use_order()));
/*
Allocate a slice of ref items that describe the items to be copied
from the first temporary table.
*/
if (alloc_ref_item_slice(thd, REF_SLICE_TMP1)) return true;
// Change sum_fields reference to calculated fields in tmp_table
if (streaming_aggregation || qep_tab[curr_tmp_table].table()->group ||
tmp_table_param.precomputed_group_by) {
if (change_to_use_tmp_fields(fields, thd, ref_items[REF_SLICE_TMP1],
&tmp_fields[REF_SLICE_TMP1],
query_block->m_added_non_hidden_fields))
return true;
} else {
if (change_to_use_tmp_fields_except_sums(
fields, thd, query_block, ref_items[REF_SLICE_TMP1],
&tmp_fields[REF_SLICE_TMP1],
query_block->m_added_non_hidden_fields))
return true;
}
curr_fields = &tmp_fields[REF_SLICE_TMP1];
// Need to set them now for correct group_fields setup, reset at the end.
set_ref_item_slice(REF_SLICE_TMP1);
qep_tab[curr_tmp_table].ref_item_slice = REF_SLICE_TMP1;
setup_tmptable_write_func(&qep_tab[curr_tmp_table], &trace_this_outer);
/*
If having is not handled here, it will be checked before the row is sent
to the client.
*/
if (having_cond &&
(streaming_aggregation ||
(exec_tmp_table->s->is_distinct && group_list.empty()))) {
/*
If there is no select distinct or rollup, then move the having to table
conds of tmp table.
NOTE : We cannot apply having after distinct. If columns of having are
not part of select distinct, then distinct may remove rows
which can satisfy having.
As this condition will read the tmp table, it is appropriate that
REF_SLICE_TMP1 is in effect when we create it below.
*/
if ((!select_distinct && rollup_state == RollupState::NONE) &&
add_having_as_tmp_table_cond(curr_tmp_table))
return true;
/*
Having condition which we are not able to add as tmp table conds are
kept as before. And, this will be applied before storing the rows in
tmp table.
*/
qep_tab[curr_tmp_table].having = having_cond;
having_cond = nullptr; // Already done
}
tmp_table_param.func_count = 0;
if (streaming_aggregation || qep_tab[curr_tmp_table].table()->group) {
tmp_table_param.func_count += tmp_table_param.sum_func_count;
tmp_table_param.sum_func_count = 0;
}
if (exec_tmp_table->group) { // Already grouped
/*
Check if group by has to respect ordering. If true, move group by to
order by.
*/
if (order.empty() && !skip_sort_order) {
for (ORDER *group = group_list.order; group; group = group->next) {
if (group->direction != ORDER_NOT_RELEVANT) {
order = group_list; /* order by group */
break;
}
}
}
group_list.clean();
}
/*
If we have different sort & group then we must sort the data by group
and copy it to a second temporary table.
This code is also used if we are using distinct something
we haven't been able to store in the temporary table yet
like SEC_TO_TIME(SUM(...)) or when distinct is used with rollup.
*/
if ((!group_list.empty() &&
(!test_if_subpart(group_list.order, order.order) || select_distinct ||
m_windowing_steps || rollup_state != RollupState::NONE)) ||
(select_distinct && (tmp_table_param.using_outer_summary_function ||
rollup_state != RollupState::NONE))) {
DBUG_PRINT("info", ("Creating group table"));
calc_group_buffer(this, group_list.order);
count_field_types(query_block, &tmp_table_param,
tmp_fields[REF_SLICE_TMP1],
select_distinct && group_list.empty(), false);
tmp_table_param.hidden_field_count =
CountHiddenFields(tmp_fields[REF_SLICE_TMP1]);
streaming_aggregation = false;
if (!exec_tmp_table->group && !exec_tmp_table->s->is_distinct) {
// 1st tmp table were materializing join result
materialize_join = true;
explain_flags.set(ESC_BUFFER_RESULT, ESP_USING_TMPTABLE);
}
curr_tmp_table++;
tmp_tables++;
Opt_trace_object trace_this_tbl(trace);
trace_this_tbl.add("adding_tmp_table_in_plan_at_position", curr_tmp_table)
.add_alnum("cause", "sorting_to_make_groups");
/* group data to new table */
/*
If the access method is loose index scan then all MIN/MAX
functions are precomputed, and should be treated as regular
functions. See extended comment above.
*/
if (qep_tab[0].range_scan() &&
is_loose_index_scan(qep_tab[0].range_scan()))
tmp_table_param.precomputed_group_by = true;
ORDER_with_src dummy; // TODO can use table->group here also
if (create_intermediate_table(&qep_tab[curr_tmp_table], *curr_fields,
dummy, true))
return true;
if (!group_list.empty()) {
explain_flags.set(group_list.src, ESP_USING_TMPTABLE);
if (!plan_is_const()) // No need to sort a single row
{
if (add_sorting_to_table(curr_tmp_table - 1, &group_list,
/*sort_before_group=*/true))
return true;
}
if (make_group_fields(this, this)) return true;
}
// Setup sum funcs only when necessary, otherwise we might break info
// for the first table
if (!group_list.empty() || tmp_table_param.sum_func_count) {
if (make_sum_func_list(*curr_fields, true, true)) return true;
const bool need_distinct =
!(qep_tab[0].range_scan() &&
is_agg_loose_index_scan(qep_tab[0].range_scan()));
if (prepare_sum_aggregators(sum_funcs, need_distinct)) return true;
group_list.clean();
if (setup_sum_funcs(thd, sum_funcs)) return true;
}
/*
Allocate a slice of ref items that describe the items to be copied
from the second temporary table.
*/
if (alloc_ref_item_slice(thd, REF_SLICE_TMP2)) return true;
// No sum funcs anymore
if (change_to_use_tmp_fields(&tmp_fields[REF_SLICE_TMP1], thd,
ref_items[REF_SLICE_TMP2],
&tmp_fields[REF_SLICE_TMP2],
query_block->m_added_non_hidden_fields))
return true;
curr_fields = &tmp_fields[REF_SLICE_TMP2];
set_ref_item_slice(REF_SLICE_TMP2);
qep_tab[curr_tmp_table].ref_item_slice = REF_SLICE_TMP2;
setup_tmptable_write_func(&qep_tab[curr_tmp_table], &trace_this_tbl);
}
if (qep_tab[curr_tmp_table].table()->s->is_distinct)
select_distinct = false; /* Each row is unique */
if (select_distinct && group_list.empty() && !m_windowing_steps) {
if (having_cond) {
qep_tab[curr_tmp_table].having = having_cond;
having_cond->update_used_tables();
having_cond = nullptr;
}
qep_tab[curr_tmp_table].needs_duplicate_removal = true;
trace_this_outer.add("reading_from_table_eliminates_duplicates", true);
explain_flags.set(ESC_DISTINCT, ESP_DUPS_REMOVAL);
select_distinct = false;
}
/* Clean tmp_table_param for the next tmp table. */
tmp_table_param.sum_func_count = tmp_table_param.func_count = 0;
tmp_table_param.cleanup();
streaming_aggregation = false;
if (!group_optimized_away) {
grouped = false;
} else {
/*
If grouping has been optimized away, a temporary table is
normally not needed unless we're explicitly requested to create
one (e.g. due to a SQL_BUFFER_RESULT hint or INSERT ... SELECT or
there is a windowing function that needs sorting).
In this case (grouping was optimized away), temp_table was
created without a grouping expression and JOIN::exec() will not
perform the necessary grouping (by the use of end_send_group()
or end_write_group()) if JOIN::group is set to false.
*/
/*
The temporary table was explicitly requested or there is a window
function which needs sorting (check need_tmp_before_win in
JOIN::optimize).
*/
assert(query_block->active_options() & OPTION_BUFFER_RESULT ||
m_windowing_steps);
// the temporary table does not have a grouping expression
assert(!qep_tab[curr_tmp_table].table()->group);
}
calc_group_buffer(this, group_list.order);
count_field_types(query_block, &tmp_table_param, *curr_fields, false,
false);
}
/*
Set up structures for a temporary table but do not actually create
the temporary table if one of these conditions are true:
- The query is implicitly grouped.
- The query is explicitly grouped and
+ implemented as a simple grouping, or
+ LIMIT 1 is specified, or
+ ROLLUP is specified, or
+ <some unknown condition>.
*/
if ((grouped || implicit_grouping) && !m_windowing_steps) {
if (make_group_fields(this, this)) return true;
if (make_sum_func_list(*curr_fields, true, true)) return true;
const bool need_distinct =
!(qep_tab && qep_tab[0].range_scan() &&
is_agg_loose_index_scan(qep_tab[0].range_scan()));
if (prepare_sum_aggregators(sum_funcs, need_distinct)) return true;
if (setup_sum_funcs(thd, sum_funcs) || thd->is_fatal_error()) return true;
}
if (qep_tab && (!group_list.empty() ||
(!order.empty() && !m_windowing_steps /* [1] */))) {
/*
[1] above: too early to do query ORDER BY if we have windowing; must
wait till after window processing.
*/
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
DBUG_PRINT("info", ("Sorting for send_result_set_metadata"));
/*
If we have already done the group, add HAVING to sorted table except
when rollup is present
*/
if (having_cond && group_list.empty() && !streaming_aggregation &&
rollup_state == RollupState::NONE) {
if (add_having_as_tmp_table_cond(curr_tmp_table)) return true;
}
if (grouped)
m_select_limit = HA_POS_ERROR;
else if (!need_tmp_before_win) {
/*
We can abort sorting after thd->select_limit rows if there are no
filter conditions for any tables after the sorted one.
Filter conditions come in several forms:
1. as a condition item attached to the join_tab, or
2. as a keyuse attached to the join_tab (ref access).
*/
for (uint i = const_tables + 1; i < primary_tables; i++) {
QEP_TAB *const tab = qep_tab + i;
if (tab->condition() || // 1
(best_ref[tab->idx()]->keyuse() &&
tab->first_inner() == NO_PLAN_IDX)) // 2
{
/* We have to sort all rows */
m_select_limit = HA_POS_ERROR;
break;
}
}
}
/*
Here we add sorting stage for ORDER BY/GROUP BY clause, if the
optimiser chose FILESORT to be faster than INDEX SCAN or there is
no suitable index present.
OPTION_FOUND_ROWS supersedes LIMIT and is taken into account.
*/
DBUG_PRINT("info", ("Sorting for order by/group by"));
ORDER_with_src order_arg = group_list.empty() ? order : group_list;
if (qep_tab &&
m_ordered_index_usage != (group_list.empty()
? ORDERED_INDEX_ORDER_BY
: ORDERED_INDEX_GROUP_BY) &&
// Windowing will change order, so it's too early to sort here
!m_windowing_steps) {
// Sort either first non-const table or the last tmp table
QEP_TAB *const sort_tab = &qep_tab[curr_tmp_table];
if (need_tmp_before_win && !materialize_join && !exec_tmp_table->group)
explain_flags.set(order_arg.src, ESP_USING_TMPTABLE);
if (add_sorting_to_table(curr_tmp_table, &order_arg,
/*sort_before_group=*/false))
return true;
/*
filesort_limit: Return only this many rows from filesort().
We can use select_limit_cnt only if we have no group_by and 1 table.
This allows us to use Bounded_queue for queries like:
"select * from t1 order by b desc limit 1;"
m_select_limit == HA_POS_ERROR (we need a full table scan)
query_expression->select_limit_cnt == 1 (we only need one row in the
result set)
*/
if (sort_tab->filesort)
sort_tab->filesort->limit =
(has_group_by || (primary_tables > curr_tmp_table + 1) ||
calc_found_rows)
? m_select_limit
: query_expression()->select_limit_cnt;
}
}
if (qep_tab && m_windowing_steps) {
for (uint wno = 0; wno < m_windows.elements; wno++) {
tmp_table_param.m_window = m_windows[wno];
if (!tmp_tables) {
curr_tmp_table = primary_tables;
tmp_tables++;
if (ref_items[REF_SLICE_SAVED_BASE].is_null()) {
/*
Make a copy of the base slice in the save slice.
This is needed because later steps will overwrite the base slice with
another slice (1-3 or window slice).
After this slice has been used, overwrite the base slice again with
the copy in the save slice.
*/
if (alloc_ref_item_slice(thd, REF_SLICE_SAVED_BASE)) return true;
copy_ref_item_slice(REF_SLICE_SAVED_BASE, REF_SLICE_ACTIVE);
current_ref_item_slice = REF_SLICE_SAVED_BASE;
}
} else {
curr_tmp_table++;
tmp_tables++;
}
ORDER_with_src dummy;
tmp_table_param.hidden_field_count = CountHiddenFields(*curr_fields);
/*
Allocate a slice of ref items that describe the items to be copied
from the next temporary table.
*/
const uint widx = REF_SLICE_WIN_1 + wno;
QEP_TAB *tab = &qep_tab[curr_tmp_table];
mem_root_deque<Item *> *orig_fields = curr_fields;
{
Opt_trace_object trace_this_tbl(trace);
trace_this_tbl
.add("adding_tmp_table_in_plan_at_position", curr_tmp_table)
.add_alnum("cause", "output_for_window_functions")
.add("with_buffer", m_windows[wno]->needs_buffering());
if (create_intermediate_table(tab, *curr_fields, dummy, false))
return true;
if (alloc_ref_item_slice(thd, widx)) return true;
if (change_to_use_tmp_fields(curr_fields, thd, ref_items[widx],
&tmp_fields[widx],
query_block->m_added_non_hidden_fields,
/*windowing*/ true))
return true;
curr_fields = &tmp_fields[widx];
set_ref_item_slice(widx);
tab->ref_item_slice = widx;
setup_tmptable_write_func(tab, &trace_this_tbl);
}
if (m_windows[wno]->needs_buffering()) {
if (CreateFramebufferTable(
thd, tmp_table_param, *query_block, *orig_fields, *curr_fields,
tab->tmp_table_param->items_to_copy, m_windows[wno])) {
return true;
}
}
if (m_windows[wno]->make_special_rows_cache(thd, tab->table()))
return true;
ORDER_with_src w_partition(m_windows[wno]->sorting_order(),
ESC_WINDOWING);
if (w_partition.order != nullptr) {
Opt_trace_object trace_pre_sort(trace, "adding_sort_to_previous_table");
if (add_sorting_to_table(curr_tmp_table - 1, &w_partition,
/*sort_before_group=*/false))
return true;
}
if (m_windows[wno]->is_last()) {
if (!order.empty() && m_ordered_index_usage != ORDERED_INDEX_ORDER_BY) {
if (add_sorting_to_table(curr_tmp_table, &order,
/*sort_before_group=*/false))
return true;
}
if (!tab->filesort && !tab->table()->s->keys &&
(!(query_block->active_options() & OPTION_BUFFER_RESULT) ||
need_tmp_before_win || wno >= 1)) {
/*
Last tmp table of execution; no sort, no duplicate elimination, no
buffering imposed by user (or it has already been implemented by
a previous tmp table): hence any row needn't be written to
tmp table's storage; send it out to query's result instead:
*/
m_windows[wno]->set_short_circuit(true);
}
}
if (having_cond != nullptr) {
tab->having = having_cond;
having_cond = nullptr;
}
}
}
// In the case of rollup (only): After the base slice list was made, we may
// have modified the field list to add rollup group items and sum switchers.
// Since there may be HAVING filters with refs that refer to the base slice,
// we need to refresh that slice (and its copy, REF_SLICE_SAVED_BASE) so
// that it includes the updated items.
//
// Note that we do this after we've made the TMP1 and TMP2 slices, since
// there's a lot of logic that looks through the GROUP BY list, which refers
// to the base slice and expects _not_ to find rollup items there.
refresh_base_slice();
fields = curr_fields;
// Reset before execution
set_ref_item_slice(REF_SLICE_SAVED_BASE);
if (qep_tab) {
qep_tab[primary_tables + tmp_tables].op_type = get_end_select_func();
}
grouped = has_group_by;
unplug_join_tabs();
/*
Tmp tables are a layer between the nested loop and the derived table's
result, WITH RECURSIVE cannot work with them. This should not happen, as a
recursive query cannot have clauses which use a tmp table (GROUP BY,
etc).
*/
assert(!query_block->is_recursive() || !tmp_tables);
cleanup_tmp_tables_on_error.release();
return false;
}
void JOIN::refresh_base_slice() {
const unsigned num_hidden_fields = CountHiddenFields(*fields);
const size_t num_select_elements = fields->size() - num_hidden_fields;
const size_t orig_num_select_elements =
num_select_elements - query_block->m_added_non_hidden_fields;
for (unsigned i = 0; i < fields->size(); ++i) {
Item *item = (*fields)[i];
size_t pos;
// See change_to_use_tmp_fields_except_sums for an explanation of how
// the visible fields, hidden fields and additional fields added by
// transformations are organized in fields and ref_item_array.
if (i < num_hidden_fields) {
pos = fields->size() - i - 1 - query_block->m_added_non_hidden_fields;
} else {
pos = i - num_hidden_fields;
if (pos >= orig_num_select_elements) pos += num_hidden_fields;
}
query_block->base_ref_items[pos] = item;
if (!ref_items[REF_SLICE_SAVED_BASE].is_null()) {
ref_items[REF_SLICE_SAVED_BASE][pos] = item;
}
}
}
void JOIN::unplug_join_tabs() {
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
map2table = nullptr;
for (uint i = 0; i < tables; ++i) best_ref[i]->cleanup();
best_ref = nullptr;
}
/**
@brief Add Filesort object to the given table to sort if with filesort
@param idx JOIN_TAB's position in the qep_tab array. The
created Filesort object gets attached to this.
@param sort_order List of expressions to sort the table by
@param sort_before_group
If true, this sort happens before grouping is done
(potentially as a step of grouping itself),
so any wrapped rollup group items should be
unwrapped.
@note This function moves tab->select, if any, to filesort->select
@return false on success, true on OOM
*/
bool JOIN::add_sorting_to_table(uint idx, ORDER_with_src *sort_order,
bool sort_before_group) {
DBUG_TRACE;
ASSERT_BEST_REF_IN_JOIN_ORDER(this);
assert(!query_block->is_recursive());
const enum join_type jt = qep_tab[idx].type();
if (jt == JT_CONST || jt == JT_EQ_REF)
return false; // 1 single row: is already sorted
// Weedout needs an underlying table to store refs from (it deduplicates
// by row ID), so if this table is part of a weedout operation, we need
// to force sorting by row IDs -- sorting rows with addon fields returns
// rows that have no reference to the underlying table object.
bool force_sort_rowids = false;
for (plan_idx i = 0; i <= static_cast<plan_idx>(idx); ++i) {
if (!qep_tab[i].starts_weedout()) {
continue;
}
plan_idx weedout_end = NO_PLAN_IDX; // Exclusive.
for (uint j = i; j < primary_tables; ++j) {
if (qep_tab[j].check_weed_out_table == qep_tab[i].flush_weedout_table) {
weedout_end = j + 1;
break;
}
}
if (weedout_end != NO_PLAN_IDX &&
weedout_end > static_cast<plan_idx>(idx)) {
force_sort_rowids = true;
break;
}
}
explain_flags.set(sort_order->src, ESP_USING_FILESORT);
QEP_TAB *const tab = &qep_tab[idx];
const bool keep_buffers =
qep_tab->join() != nullptr &&
qep_tab->join()->query_block->master_query_expression()->item !=
nullptr &&
qep_tab->join()
->query_block->master_query_expression()
->item->is_uncacheable();
{
// Switch to the right slice if applicable, so that we fetch out the correct
// items from order_arg.
const Switch_ref_item_slice slice_switch(this, tab->ref_item_slice);
tab->filesort = new (thd->mem_root)
Filesort(thd, {tab->table()}, keep_buffers, sort_order->order,
HA_POS_ERROR, /*remove_duplicates=*/false, force_sort_rowids,
/*unwrap_rollup=*/sort_before_group);
tab->filesort_pushed_order = sort_order->order;
}
if (!tab->filesort) return true;
Opt_trace_object trace_tmp(&thd->opt_trace, "filesort");
trace_tmp.add_alnum("adding_sort_to_table",
tab->table() ? tab->table()->alias : "");
return false;
}
/**
Find a cheaper access key than a given key.
@param tab NULL or JOIN_TAB of the accessed table
@param order Linked list of ORDER BY arguments
@param table Table if tab == NULL or tab->table()
@param usable_keys Key map to find a cheaper key in
@param ref_key
* 0 <= key < MAX_KEY - key number (hint) to start the search
* -1 - no key number provided
@param select_limit LIMIT value, or HA_POS_ERROR if no limit
@param [out] new_key Key number if success, otherwise undefined
@param [out] new_key_direction Return -1 (reverse) or +1 if success,
otherwise undefined
@param [out] new_select_limit Return adjusted LIMIT
@param [out] new_used_key_parts NULL by default, otherwise return number
of new_key prefix columns if success
or undefined if the function fails
@param [out] saved_best_key_parts NULL by default, otherwise preserve the
value for further use in
ReverseIndexRangeScanIterator
@param [out] new_read_time NULL by default, otherwise return the
cost of access using new_key if success
or undefined if the function fails
@note
This function takes into account table->quick_condition_rows statistic
(that is calculated by JOIN::make_join_plan()).
However, single table procedures such as mysql_update() and mysql_delete()
never call JOIN::make_join_plan(), so they have to update it manually
(@see get_index_for_order()).
This function resets bits in TABLE::quick_keys for indexes with mixed
ASC/DESC keyparts as range scan doesn't support range reordering
required for them.
*/
bool test_if_cheaper_ordering(const JOIN_TAB *tab, ORDER_with_src *order,
TABLE *table, Key_map usable_keys, int ref_key,
ha_rows select_limit, int *new_key,
int *new_key_direction, ha_rows *new_select_limit,
uint *new_used_key_parts,
uint *saved_best_key_parts,
double *new_read_time) {
DBUG_TRACE;
/*
Check whether there is an index compatible with the given order
usage of which is cheaper than usage of the ref_key index (ref_key>=0)
or a table scan.
It may be the case if ORDER/GROUP BY is used with LIMIT.
*/
ha_rows best_select_limit = HA_POS_ERROR;
JOIN *join = tab ? tab->join() : nullptr;
if (join) ASSERT_BEST_REF_IN_JOIN_ORDER(join);
uint nr;
uint best_key_parts = 0;
int best_key_direction = 0;
ha_rows best_records = 0;
double best_read_time = 0;
double read_time;
int best_key = -1;
bool is_best_covering = false;
double fanout = 1;
const ha_rows table_records = table->file->stats.records;
const bool group = join && join->grouped && order == &join->group_list;
double refkey_rows_estimate =
static_cast<double>(table->quick_condition_rows);
const bool has_limit = (select_limit != HA_POS_ERROR);
const join_type cur_access_method = tab ? tab->type() : JT_ALL;
if (join) {
read_time = tab->position()->read_cost;
for (uint jt = tab->idx() + 1; jt < join->primary_tables; jt++) {
POSITION *pos = join->best_ref[jt]->position();
fanout *= pos->rows_fetched * pos->filter_effect;
if (fanout < 0) break; // fanout became 'unknown'
}
} else
read_time = table->file->table_scan_cost().total_cost();
/*
Calculate the selectivity of the ref_key for REF_ACCESS. For
RANGE_ACCESS we use table->quick_condition_rows.
*/
if (ref_key >= 0 && cur_access_method == JT_REF) {
if (table->quick_keys.is_set(ref_key))
refkey_rows_estimate = static_cast<double>(table->quick_rows[ref_key]);
else {
const KEY *ref_keyinfo = table->key_info + ref_key;
if (ref_keyinfo->has_records_per_key(tab->ref().key_parts - 1))
refkey_rows_estimate =
ref_keyinfo->records_per_key(tab->ref().key_parts - 1);
else
refkey_rows_estimate = 1.0; // No index statistics
}
assert(refkey_rows_estimate >= 1.0);
}
for (nr = 0; nr < table->s->keys; nr++) {
int direction = 0;
uint used_key_parts;
bool skip_quick;
if (usable_keys.is_set(nr) &&
(direction = test_if_order_by_key(order, table, nr, &used_key_parts,
&skip_quick))) {
const bool is_covering = table->covering_keys.is_set(nr) ||
(nr == table->s->primary_key &&
table->file->primary_key_is_clustered());
// Don't allow backward scans on indexes with mixed ASC/DESC key parts
if (skip_quick) table->quick_keys.clear_bit(nr);
/*
Don't use an index scan with ORDER BY without limit.
For GROUP BY without limit always use index scan
if there is a suitable index.
Why we hold to this asymmetry hardly can be explained
rationally. It's easy to demonstrate that using
temporary table + filesort could be cheaper for grouping
queries too.
*/
if (is_covering || select_limit != HA_POS_ERROR ||
(ref_key < 0 && (group || table->force_index_order))) {
rec_per_key_t rec_per_key;
KEY *keyinfo = table->key_info + nr;
if (select_limit == HA_POS_ERROR) select_limit = table_records;
if (group) {
/*
Used_key_parts can be larger than keyinfo->key_parts
when using a secondary index clustered with a primary
key (e.g. as in Innodb).
See Bug #28591 for details.
*/
rec_per_key =
used_key_parts && used_key_parts <= actual_key_parts(keyinfo)
? keyinfo->records_per_key(used_key_parts - 1)
: 1.0f;
rec_per_key = std::max(rec_per_key, 1.0f);
/*
With a grouping query each group containing on average
rec_per_key records produces only one row that will
be included into the result set.
*/
if (select_limit > table_records / rec_per_key)
select_limit = table_records;
else
select_limit = (ha_rows)(select_limit * rec_per_key);
}
/*
If tab=tk is not the last joined table tn then to get first
L records from the result set we can expect to retrieve
only L/fanout(tk,tn) where fanout(tk,tn) says how many
rows in the record set on average will match each row tk.
Usually our estimates for fanouts are too pessimistic.
So the estimate for L/fanout(tk,tn) will be too optimistic
and as result we'll choose an index scan when using ref/range
access + filesort will be cheaper.
*/
if (fanout == 0) { // Would have been a division-by-zero
select_limit = HA_POS_ERROR; // -> 'infinite'
} else if (fanout >= 0) { // 'fanout' not unknown
const double new_limit = max(select_limit / fanout, 1.0);
if (new_limit >= static_cast<double>(HA_POS_ERROR)) {
select_limit = HA_POS_ERROR;
} else {
select_limit = new_limit;
}
}
/*
We assume that each of the tested indexes is not correlated
with ref_key. Thus, to select first N records we have to scan
N/selectivity(ref_key) index entries.
selectivity(ref_key) = #scanned_records/#table_records =
refkey_rows_estimate/table_records.
In any case we can't select more than #table_records.
N/(refkey_rows_estimate/table_records) > table_records
<=> N > refkey_rows_estimate.
Neither should it be possible to select more than #table_records
rows from refkey_rows_estimate.
*/
if (select_limit > refkey_rows_estimate)
select_limit = table_records;
else if (table_records >= refkey_rows_estimate)
select_limit = (ha_rows)(select_limit * (double)table_records /
refkey_rows_estimate);
rec_per_key =
keyinfo->records_per_key(keyinfo->user_defined_key_parts - 1);
rec_per_key = std::max(rec_per_key, 1.0f);
/*
Here we take into account the fact that rows are
accessed in sequences rec_per_key records in each.
Rows in such a sequence are supposed to be ordered
by rowid/primary key. When reading the data
in a sequence we'll touch not more pages than the
table file contains.
TODO. Use the formula for a disk sweep sequential access
to calculate the cost of accessing data rows for one
index entry.
*/
const Cost_estimate table_scan_time = table->file->table_scan_cost();
const double index_scan_time =
select_limit / rec_per_key *
min<double>(table->file->page_read_cost(nr, rec_per_key),
table_scan_time.total_cost());
/*
Switch to index that gives order if its scan time is smaller than
read_time of current chosen access method. In addition, if the
current chosen access method is index scan or table scan, always
switch to the index that gives order when it is covering or when
force index order or group by is present.
*/
if (((cur_access_method == JT_ALL ||
cur_access_method == JT_INDEX_SCAN) &&
(is_covering || group || table->force_index_order)) ||
index_scan_time < read_time) {
ha_rows quick_records = table_records;
const ha_rows refkey_select_limit =
(ref_key >= 0 && table->covering_keys.is_set(ref_key))
? static_cast<ha_rows>(refkey_rows_estimate)
: HA_POS_ERROR;
if ((is_best_covering && !is_covering) ||
(is_covering && refkey_select_limit < select_limit))
continue;
if (table->quick_keys.is_set(nr))
quick_records = table->quick_rows[nr];
if (best_key < 0 ||
(select_limit <= min(quick_records, best_records)
? keyinfo->user_defined_key_parts < best_key_parts
: quick_records < best_records) ||
// We assume forward scan is faster than backward even if the
// key is longer. This should be taken into account in cost
// calculation.
direction > best_key_direction) {
best_key = nr;
best_key_parts = keyinfo->user_defined_key_parts;
if (saved_best_key_parts) *saved_best_key_parts = used_key_parts;
best_read_time = index_scan_time;
best_records = quick_records;
is_best_covering = is_covering;
best_key_direction = direction;
best_select_limit = select_limit;
}
}
}
}
}
if (best_key < 0 || best_key == ref_key) return false;
*new_key = best_key;
*new_key_direction = best_key_direction;
*new_select_limit = has_limit ? best_select_limit : table_records;
if (new_used_key_parts != nullptr) *new_used_key_parts = best_key_parts;
if (new_read_time) *new_read_time = best_read_time;
return true;
}
/**
Find a key to apply single table UPDATE/DELETE by a given ORDER
@param order Linked list of ORDER BY arguments
@param table Table to find a key
@param limit LIMIT clause parameter
@param range_scan Range scan used for this table, if any
@param [out] need_sort true if filesort needed
@param [out] reverse
true if the key is reversed again given ORDER (undefined if key == MAX_KEY)
@return
- MAX_KEY if no key found (need_sort == true)
- MAX_KEY if quick select result order is OK (need_sort == false)
- key number (either index scan or quick select) (need_sort == false)
@note
Side effects:
- may deallocate or deallocate and replace select->quick;
- may set table->quick_condition_rows and table->quick_rows[...]
to table->file->stats.records.
*/
uint get_index_for_order(ORDER_with_src *order, TABLE *table, ha_rows limit,
AccessPath *range_scan, bool *need_sort,
bool *reverse) {
if (range_scan &&
unique_key_range(range_scan)) { // Single row select (always
// "ordered"): Ok to use with
// key field UPDATE
*need_sort = false;
/*
Returning of MAX_KEY here prevents updating of used_key_is_modified
in mysql_update(). Use AccessPath "as is".
*/
return MAX_KEY;
}
if (order->empty()) {
*need_sort = false;
if (range_scan)
return used_index(range_scan); // index or MAX_KEY, use AccessPath as is
else
return table->file
->key_used_on_scan; // MAX_KEY or index for some engines
}
if (!is_simple_order(order->order)) // just to cut further expensive checks
{
*need_sort = true;
return MAX_KEY;
}
if (range_scan) {
if (used_index(range_scan) == MAX_KEY) {
*need_sort = true;
return MAX_KEY;
}
uint used_key_parts;
bool skip_path;
switch (test_if_order_by_key(order, table, used_index(range_scan),
&used_key_parts, &skip_path)) {
case 1: // desired order
*need_sort = false;
return used_index(range_scan);
case 0: // unacceptable order
*need_sort = true;
return MAX_KEY;
case -1: // desired order, but opposite direction
{
if (!skip_path && !make_reverse(used_key_parts, range_scan)) {
*need_sort = false;
return used_index(range_scan);
} else {
*need_sort = true;
return MAX_KEY;
}
}
}
assert(0);
} else if (limit != HA_POS_ERROR) { // check if some index scan & LIMIT is
// more efficient than filesort
/*
Update quick_condition_rows since single table UPDATE/DELETE procedures
don't call JOIN::make_join_plan() and leave this variable uninitialized.
*/
table->quick_condition_rows = table->file->stats.records;
int key, direction;
if (test_if_cheaper_ordering(nullptr, order, table,
table->keys_in_use_for_order_by, -1, limit,
&key, &direction, &limit)) {
*need_sort = false;
*reverse = (direction < 0);
return key;
}
}
*need_sort = true;
return MAX_KEY;
}
/**
Returns number of key parts depending on
OPTIMIZER_SWITCH_USE_INDEX_EXTENSIONS flag.
@param key_info pointer to KEY structure
@return number of key parts.
*/
uint actual_key_parts(const KEY *key_info) {
return current_thd->optimizer_switch_flag(
OPTIMIZER_SWITCH_USE_INDEX_EXTENSIONS)
? key_info->actual_key_parts
: key_info->user_defined_key_parts;
}
uint actual_key_flags(const KEY *key_info) {
return current_thd->optimizer_switch_flag(
OPTIMIZER_SWITCH_USE_INDEX_EXTENSIONS)
? key_info->actual_flags
: key_info->flags;
}
join_type calc_join_type(AccessPath *path) {
switch (path->type) {
case AccessPath::INDEX_RANGE_SCAN:
case AccessPath::INDEX_SKIP_SCAN:
case AccessPath::GROUP_INDEX_SKIP_SCAN:
return JT_RANGE;
case AccessPath::INDEX_MERGE:
case AccessPath::ROWID_INTERSECTION:
case AccessPath::ROWID_UNION:
return JT_INDEX_MERGE;
default:
assert(false);
return JT_RANGE;
}
}
/**
@} (end of group Query_Optimizer)
*/
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