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postgres_fdw: Report warning when timeout expires while getting query result.

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When aborting remote transaction or sending cancel request to a remote server,
postgres_fdw calls pgfdw_get_cleanup_result() to wait for the result of
transaction abort query or cancel request to arrive. It fails to get the result
if the timeout expires or a connection trouble happens.

Previously postgres_fdw reported no warning message even when the timeout
expired or a connection trouble happened in pgfdw_get_cleanup_result().
This could make the troubleshooting harder when such an event occurred.

This commit makes pgfdw_get_cleanup_result() tell its caller what trouble
(timeout or connection error) occurred, on failure, and also makes its caller
report the proper warning message based on that information.

Author: Fujii Masao
Reviewed-by: Bharath Rupireddy
Discussion: https://postgr.es/m/15aa988c-722e-ad3e-c936-4420c5b2bfea@oss.nttdata.com
This commit is contained in:
Fujii Masao 2021-12-08 23:31:46 +09:00
parent d6f96ed94e
commit 815d61fcd4
1 changed files with 39 additions and 12 deletions
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51
contrib/postgres_fdw/connection.c
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@ -104,7 +104,7 @@ static bool pgfdw_cancel_query(PGconn *conn);
static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query, static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query,
bool ignore_errors); bool ignore_errors);
static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
PGresult **result); PGresult **result, bool *timed_out);
static void pgfdw_abort_cleanup(ConnCacheEntry *entry, const char *sql, static void pgfdw_abort_cleanup(ConnCacheEntry *entry, const char *sql,
bool toplevel); bool toplevel);
static bool UserMappingPasswordRequired(UserMapping *user); static bool UserMappingPasswordRequired(UserMapping *user);
@ -1154,6 +1154,7 @@ pgfdw_cancel_query(PGconn *conn)
char errbuf[256]; char errbuf[256];
PGresult *result = NULL; PGresult *result = NULL;
TimestampTz endtime; TimestampTz endtime;
bool timed_out;
/* /*
* If it takes too long to cancel the query and discard the result, assume * If it takes too long to cancel the query and discard the result, assume
@ -1180,8 +1181,19 @@ pgfdw_cancel_query(PGconn *conn)
} }
/* Get and discard the result of the query. */ /* Get and discard the result of the query. */
if (pgfdw_get_cleanup_result(conn, endtime, &result)) if (pgfdw_get_cleanup_result(conn, endtime, &result, &timed_out))
{
if (timed_out)
ereport(WARNING,
(errmsg("could not get result of cancel request due to timeout")));
else
ereport(WARNING,
(errcode(ERRCODE_CONNECTION_FAILURE),
errmsg("could not get result of cancel request: %s",
pchomp(PQerrorMessage(conn)))));
return false; return false;
}
PQclear(result); PQclear(result);
return true; return true;
@ -1204,6 +1216,7 @@ pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors)
{ {
PGresult *result = NULL; PGresult *result = NULL;
TimestampTz endtime; TimestampTz endtime;
bool timed_out;
/* /*
* If it takes too long to execute a cleanup query, assume the connection * If it takes too long to execute a cleanup query, assume the connection
@ -1224,8 +1237,17 @@ pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors)
} }
/* Get the result of the query. */ /* Get the result of the query. */
if (pgfdw_get_cleanup_result(conn, endtime, &result)) if (pgfdw_get_cleanup_result(conn, endtime, &result, &timed_out))
{
if (timed_out)
ereport(WARNING,
(errmsg("could not get query result due to timeout"),
query ? errcontext("remote SQL command: %s", query) : 0));
else
pgfdw_report_error(WARNING, NULL, conn, false, query);
return false; return false;
}
/* Issue a warning if not successful. */ /* Issue a warning if not successful. */
if (PQresultStatus(result) != PGRES_COMMAND_OK) if (PQresultStatus(result) != PGRES_COMMAND_OK)
@ -1245,15 +1267,19 @@ pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors)
* side back to the appropriate state. * side back to the appropriate state.
* *
* endtime is the time at which we should give up and assume the remote * endtime is the time at which we should give up and assume the remote
* side is dead. Returns true if the timeout expired, otherwise false. * side is dead. Returns true if the timeout expired or connection trouble
* Sets *result except in case of a timeout. * occurred, false otherwise. Sets *result except in case of a timeout.
* Sets timed_out to true only when the timeout expired.
*/ */
static bool static bool
pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result) pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result,
bool *timed_out)
{ {
volatile bool timed_out = false; volatile bool failed = false;
PGresult *volatile last_res = NULL; PGresult *volatile last_res = NULL;
*timed_out = false;
/* In what follows, do not leak any PGresults on an error. */ /* In what follows, do not leak any PGresults on an error. */
PG_TRY(); PG_TRY();
{ {
@ -1271,7 +1297,8 @@ pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result)
cur_timeout = TimestampDifferenceMilliseconds(now, endtime); cur_timeout = TimestampDifferenceMilliseconds(now, endtime);
if (cur_timeout <= 0) if (cur_timeout <= 0)
{ {
timed_out = true; *timed_out = true;
failed = true;
goto exit; goto exit;
} }
@ -1290,8 +1317,8 @@ pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result)
{ {
if (!PQconsumeInput(conn)) if (!PQconsumeInput(conn))
{ {
/* connection trouble; treat the same as a timeout */ /* connection trouble */
timed_out = true; failed = true;
goto exit; goto exit;
} }
} }
@ -1313,11 +1340,11 @@ exit: ;
} }
PG_END_TRY(); PG_END_TRY();
if (timed_out) if (failed)
PQclear(last_res); PQclear(last_res);
else else
*result = last_res; *result = last_res;
return timed_out; return failed;
} }
/* /*