Reimplement nullification of walsender timestamp

alvherre · alvherre · commit 20c4df8c8d7c · 2020-01-08T14:33:49.000-03:00
Make the value null only at pg_stat_activity-output time, as suggested by Tom Lane, instead of messing with the internal state. This should appease buildfarm members with force_parallel_mode=regress, which are running parallel queries on logical replication walsenders. The fact that walsenders can run parallel queries should perhaps be studied more carefully, but for the moment let's get rid of the red blots in buildfarm. Backpatch to pg10, like the previous commit. Discussion: https://postgr.es/m/30804.1578438763@sss.pgh.pa.us
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -817,13 +817,6 @@ GetCurrentTransactionStopTimestamp(void)
 void
 SetCurrentStatementStartTimestamp(void)
 {
-	/*
-	 * Skip if on a walsender; this is not needed, and it confuses monitoring
-	 * if we publish non-NULL values.
-	 */
-	if (am_walsender)
-		return;
-
 	if (!IsParallelWorker())
 		stmtStartTimestamp = GetCurrentTimestamp();
 	else
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
@@ -726,7 +726,13 @@ pg_stat_get_activity(PG_FUNCTION_ARGS)
 			else
 				nulls[7] = true;
 
-			if (beentry->st_xact_start_timestamp != 0)
+			/*
+			 * Don't expose transaction time for walsenders; it confuses
+			 * monitoring, particularly because we don't keep the time up-to-
+			 * date.
+			 */
+			if (beentry->st_xact_start_timestamp != 0 &&
+				beentry->st_backendType != B_WAL_SENDER)
 				values[8] = TimestampTzGetDatum(beentry->st_xact_start_timestamp);
 			else
 				nulls[8] = true;
