database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-06-13 07:41:39 +03:00
Code Activity

libpq-be-fe-helpers.h: wrap new cancel APIs

Browse Source 
Commit 61461a300c introduced new functions to libpq for cancelling
queries.  This commit introduces a helper function that backend-side
libraries and extensions can use to invoke those.  This function takes a
timeout and can itself be interrupted while it is waiting for a cancel
request to be sent and processed, instead of being blocked.

This replaces the usage of the old functions in postgres_fdw and dblink.

Finally, it also adds some test coverage for the cancel support in
postgres_fdw.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/CAGECzQT_VgOWWENUqvUV9xQmbaCyXjtRRAYO8W07oqashk_N+g@mail.gmail.com
This commit is contained in:
Alvaro Herrera
2024-03-28 11:31:03 +01:00
parent 427005742b
commit 2466d6654f
5 changed files with 140 additions and 39 deletions
Download Patch File Download Diff File Expand all files Collapse all files

47
contrib/postgres_fdw/connection.c
View File

@ -133,7 +133,7 @@ static void pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue);
static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry);
static void pgfdw_reset_xact_state(ConnCacheEntry *entry, bool toplevel);
static bool pgfdw_cancel_query(PGconn *conn);
static bool pgfdw_cancel_query_begin(PGconn *conn);
static bool pgfdw_cancel_query_begin(PGconn *conn, TimestampTz endtime);
static bool pgfdw_cancel_query_end(PGconn *conn, TimestampTz endtime,
bool consume_input);
static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query,
@ -1315,36 +1315,31 @@ pgfdw_cancel_query(PGconn *conn)
endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
CONNECTION_CLEANUP_TIMEOUT);
if (!pgfdw_cancel_query_begin(conn))
if (!pgfdw_cancel_query_begin(conn, endtime))
return false;
return pgfdw_cancel_query_end(conn, endtime, false);
}
/*
* Submit a cancel request to the given connection, waiting only until
* the given time.
*
* We sleep interruptibly until we receive confirmation that the cancel
* request has been accepted, and if it is, return true; if the timeout
* lapses without that, or the request fails for whatever reason, return
* false.
*/
static bool
pgfdw_cancel_query_begin(PGconn *conn)
pgfdw_cancel_query_begin(PGconn *conn, TimestampTz endtime)
{
PGcancel *cancel;
char errbuf[256];
char *errormsg = libpqsrv_cancel(conn, endtime);
/*
* Issue cancel request. Unfortunately, there's no good way to limit the
* amount of time that we might block inside PQgetCancel().
*/
if ((cancel = PQgetCancel(conn)))
{
if (!PQcancel(cancel, errbuf, sizeof(errbuf)))
{
ereport(WARNING,
(errcode(ERRCODE_CONNECTION_FAILURE),
errmsg("could not send cancel request: %s",
errbuf)));
PQfreeCancel(cancel);
return false;
}
PQfreeCancel(cancel);
}
if (errormsg != NULL)
ereport(WARNING,
errcode(ERRCODE_CONNECTION_FAILURE),
errmsg("could not send cancel request: %s", errormsg));
return true;
return errormsg == NULL;
}
static bool
@ -1685,7 +1680,11 @@ pgfdw_abort_cleanup_begin(ConnCacheEntry *entry, bool toplevel,
*/
if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE)
{
if (!pgfdw_cancel_query_begin(entry->conn))
TimestampTz endtime;
endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(),
CONNECTION_CLEANUP_TIMEOUT);
if (!pgfdw_cancel_query_begin(entry->conn, endtime))
return false; /* Unable to cancel running query */
*cancel_requested = lappend(*cancel_requested, entry);
}

15
contrib/postgres_fdw/expected/postgres_fdw.out
View File

@ -2739,6 +2739,21 @@ SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c
(10 rows)
ALTER VIEW v4 OWNER TO regress_view_owner;
-- Make sure this big CROSS JOIN query is pushed down
EXPLAIN (VERBOSE, COSTS OFF) SELECT count(*) FROM ft1 CROSS JOIN ft2 CROSS JOIN ft4 CROSS JOIN ft5;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------------------------
Foreign Scan
Output: (count(*))
Relations: Aggregate on ((((public.ft1) INNER JOIN (public.ft2)) INNER JOIN (public.ft4)) INNER JOIN (public.ft5))
Remote SQL: SELECT count(*) FROM ((("S 1"."T 1" r1 INNER JOIN "S 1"."T 1" r2 ON (TRUE)) INNER JOIN "S 1"."T 3" r4 ON (TRUE)) INNER JOIN "S 1"."T 4" r6 ON (TRUE))
(4 rows)
-- Make sure query cancellation works
SET statement_timeout = '10ms';
select count(*) from ft1 CROSS JOIN ft2 CROSS JOIN ft4 CROSS JOIN ft5; -- this takes very long
ERROR: canceling statement due to statement timeout
RESET statement_timeout;
-- ====================================================================
-- Check that userid to use when querying the remote table is correctly
-- propagated into foreign rels present in subqueries under an UNION ALL

7
contrib/postgres_fdw/sql/postgres_fdw.sql
View File

@ -737,6 +737,13 @@ SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c
SELECT t1.c1, t2.c2 FROM v4 t1 LEFT JOIN ft5 t2 ON (t1.c1 = t2.c1) ORDER BY t1.c1, t2.c1 OFFSET 10 LIMIT 10;
ALTER VIEW v4 OWNER TO regress_view_owner;
-- Make sure this big CROSS JOIN query is pushed down
EXPLAIN (VERBOSE, COSTS OFF) SELECT count(*) FROM ft1 CROSS JOIN ft2 CROSS JOIN ft4 CROSS JOIN ft5;
-- Make sure query cancellation works
SET statement_timeout = '10ms';
select count(*) from ft1 CROSS JOIN ft2 CROSS JOIN ft4 CROSS JOIN ft5; -- this takes very long
RESET statement_timeout;
-- ====================================================================
-- Check that userid to use when querying the remote table is correctly
-- propagated into foreign rels present in subqueries under an UNION ALL