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

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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
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47
contrib/postgres_fdw/connection.c
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@ -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);
}