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Make dblink interruptible, via new libpqsrv APIs.

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This replaces dblink's blocking libpq calls, allowing cancellation and
allowing DROP DATABASE (of a database not involved in the query).  Apart
from explicit dblink_cancel_query() calls, dblink still doesn't cancel
the remote side.  The replacement for the blocking calls consists of
new, general-purpose query execution wrappers in the libpqsrv facility.
Out-of-tree extensions should adopt these.  Use them in postgres_fdw,
replacing a local implementation from which the libpqsrv implementation
derives.  This is a bug fix for dblink.  Code inspection identified the
bug at least thirteen years ago, but user complaints have not appeared.
Hence, no back-patch for now.

Discussion: https://postgr.es/m/20231122012945.74@rfd.leadboat.com
This commit is contained in:
Noah Misch 2024-01-08 11:39:56 -08:00
parent 0efc831847
commit d3c5f37dd5
8 changed files with 180 additions and 95 deletions
Download patch file Download diff file Expand all files Collapse all files

28
contrib/dblink/dblink.c
View file

@ -61,6 +61,7 @@
#include "utils/memutils.h"
#include "utils/rel.h"
#include "utils/varlena.h"
#include "utils/wait_event.h"
PG_MODULE_MAGIC;
@ -133,6 +134,7 @@ static HTAB *remoteConnHash = NULL;
/* custom wait event values, retrieved from shared memory */
static uint32 dblink_we_connect = 0;
static uint32 dblink_we_get_conn = 0;
static uint32 dblink_we_get_result = 0;
/*
* Following is list that holds multiple remote connections.
@ -252,6 +254,9 @@ dblink_init(void)
{
if (!pconn)
{
if (dblink_we_get_result == 0)
dblink_we_get_result = WaitEventExtensionNew("DblinkGetResult");
pconn = (remoteConn *) MemoryContextAlloc(TopMemoryContext, sizeof(remoteConn));
pconn->conn = NULL;
pconn->openCursorCount = 0;
@ -442,7 +447,7 @@ dblink_open(PG_FUNCTION_ARGS)
/* If we are not in a transaction, start one */
if (PQtransactionStatus(conn) == PQTRANS_IDLE)
{
res = PQexec(conn, "BEGIN");
res = libpqsrv_exec(conn, "BEGIN", dblink_we_get_result);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
dblink_res_internalerror(conn, res, "begin error");
PQclear(res);
@ -461,7 +466,7 @@ dblink_open(PG_FUNCTION_ARGS)
(rconn->openCursorCount)++;
appendStringInfo(&buf, "DECLARE %s CURSOR FOR %s", curname, sql);
res = PQexec(conn, buf.data);
res = libpqsrv_exec(conn, buf.data, dblink_we_get_result);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
dblink_res_error(conn, conname, res, fail,
@ -530,7 +535,7 @@ dblink_close(PG_FUNCTION_ARGS)
appendStringInfo(&buf, "CLOSE %s", curname);
/* close the cursor */
res = PQexec(conn, buf.data);
res = libpqsrv_exec(conn, buf.data, dblink_we_get_result);
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
dblink_res_error(conn, conname, res, fail,
@ -550,7 +555,7 @@ dblink_close(PG_FUNCTION_ARGS)
{
rconn->newXactForCursor = false;
res = PQexec(conn, "COMMIT");
res = libpqsrv_exec(conn, "COMMIT", dblink_we_get_result);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
dblink_res_internalerror(conn, res, "commit error");
PQclear(res);
@ -632,7 +637,7 @@ dblink_fetch(PG_FUNCTION_ARGS)
* PGresult will be long-lived even though we are still in a short-lived
* memory context.
*/
res = PQexec(conn, buf.data);
res = libpqsrv_exec(conn, buf.data, dblink_we_get_result);
if (!res ||
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
@ -780,7 +785,7 @@ dblink_record_internal(FunctionCallInfo fcinfo, bool is_async)
else
{
/* async result retrieval, do it the old way */
PGresult *res = PQgetResult(conn);
PGresult *res = libpqsrv_get_result(conn, dblink_we_get_result);
/* NULL means we're all done with the async results */
if (res)
@ -1088,7 +1093,8 @@ materializeQueryResult(FunctionCallInfo fcinfo,
PQclear(sinfo.last_res);
PQclear(sinfo.cur_res);
/* and clear out any pending data in libpq */
while ((res = PQgetResult(conn)) != NULL)
while ((res = libpqsrv_get_result(conn, dblink_we_get_result)) !=
NULL)
PQclear(res);
PG_RE_THROW();
}
@ -1115,7 +1121,7 @@ storeQueryResult(volatile storeInfo *sinfo, PGconn *conn, const char *sql)
{
CHECK_FOR_INTERRUPTS();
sinfo->cur_res = PQgetResult(conn);
sinfo->cur_res = libpqsrv_get_result(conn, dblink_we_get_result);
if (!sinfo->cur_res)
break;
@ -1443,7 +1449,7 @@ dblink_exec(PG_FUNCTION_ARGS)
if (!conn)
dblink_conn_not_avail(conname);
res = PQexec(conn, sql);
res = libpqsrv_exec(conn, sql, dblink_we_get_result);
if (!res ||
(PQresultStatus(res) != PGRES_COMMAND_OK &&
PQresultStatus(res) != PGRES_TUPLES_OK))
@ -2739,8 +2745,8 @@ dblink_res_error(PGconn *conn, const char *conname, PGresult *res,
/*
* If we don't get a message from the PGresult, try the PGconn. This is
* needed because for connection-level failures, PQexec may just return
* NULL, not a PGresult at all.
* needed because for connection-level failures, PQgetResult may just
* return NULL, not a PGresult at all.
*/
if (message_primary == NULL)
message_primary = pchomp(PQerrorMessage(conn));