Move isolationtester's is-blocked query into C code for speed.

Commit 4deb41381 modified isolationtester's query to see whether a
session is blocked to also check for waits occurring in GetSafeSnapshot.
However, it did that in a way that enormously increased the query's
runtime under CLOBBER_CACHE_ALWAYS, causing the buildfarm members
that use that to run about four times slower than before, and in some
cases fail entirely.  To fix, push the entire logic into a dedicated
backend function.  This should actually reduce the CLOBBER_CACHE_ALWAYS
runtime from what it was previously, though I've not checked that.

In passing, expose a SQL function to check for safe-snapshot blockage,
comparable to pg_blocking_pids.  This is more or less free given the
infrastructure built to solve the other problem, so we might as well.

Thomas Munro

Discussion: https://postgr.es/m/20170407165749.pstcakbc637opkax@alap3.anarazel.de

1 files changed, 2 insertions, 10 deletions

diff --git a/src/test/isolation/isolationtester.c b/src/test/isolation/isolationtester.c
index 4d18710bdfd..3af5a706ce9 100644
--- a/src/test/isolation/isolationtester.c
+++ b/src/test/isolation/isolationtester.c
@@ -224,20 +224,12 @@ main(int argc, char **argv)
 	 */
 	initPQExpBuffer(&wait_query);
 	appendPQExpBufferStr(&wait_query,
-						 "SELECT pg_catalog.pg_blocking_pids($1) && '{");
+			"SELECT pg_catalog.pg_isolation_test_session_is_blocked($1, '{");
 	/* The spec syntax requires at least one session; assume that here. */
 	appendPQExpBufferStr(&wait_query, backend_pids[1]);
 	for (i = 2; i < nconns; i++)
 		appendPQExpBuffer(&wait_query, ",%s", backend_pids[i]);
-	appendPQExpBufferStr(&wait_query, "}'::integer[]");
-
-	/* Also detect certain wait events. */
-	appendPQExpBufferStr(&wait_query,
-						 " OR EXISTS ("
-						 "  SELECT * "
-						 "  FROM pg_catalog.pg_stat_activity "
-						 "  WHERE pid = $1 "
-						 "  AND wait_event IN ('SafeSnapshot'))");
+	appendPQExpBufferStr(&wait_query, "}')");
 
 	res = PQprepare(conns[0], PREP_WAITING, wait_query.data, 0, NULL);
 	if (PQresultStatus(res) != PGRES_COMMAND_OK)