Fix handling of pgstat counters for TRUNCATE in a prepared transaction.

tglsfdc · tglsfdc · commit 81e82a2bd488 · 2016-10-13T19:46:05.000-04:00
pgstat_twophase_postcommit is supposed to duplicate the math in AtEOXact_PgStat, but it had missed out the bit about clearing t_delta_live_tuples/t_delta_dead_tuples for a TRUNCATE. It's harder than you might think to replicate the issue here, because those counters would only be nonzero when a previous transaction in the same backend had added/deleted tuples in the truncated table, and those counts hadn't been sent to the stats collector yet. Evident oversight in commit d42358e. I've not added a regression test for this; we tried to add one in d42358e, and had to revert it because it was too timing-sensitive for the buildfarm. Back-patch to 9.5 where d42358e came in. Stas Kelvich Discussion: <EB57BF68-C06D-4737-BDDC-4BA778F4E62B@postgrespro.ru>
diff --git a/src/backend/postmaster/pgstat.c b/src/backend/postmaster/pgstat.c
@@ -2226,7 +2226,12 @@ pgstat_twophase_postcommit(TransactionId xid, uint16 info,
 	pgstat_info->t_counts.t_tuples_updated += rec->tuples_updated;
 	pgstat_info->t_counts.t_tuples_deleted += rec->tuples_deleted;
 	pgstat_info->t_counts.t_truncated = rec->t_truncated;
-
+	if (rec->t_truncated)
+	{
+		/* forget live/dead stats seen by backend thus far */
+		pgstat_info->t_counts.t_delta_live_tuples = 0;
+		pgstat_info->t_counts.t_delta_dead_tuples = 0;
+	}
 	pgstat_info->t_counts.t_delta_live_tuples +=
 		rec->tuples_inserted - rec->tuples_deleted;
 	pgstat_info->t_counts.t_delta_dead_tuples +=
