pg_stat_activity: show NULL stmt start time for walsenders

alvherre · alvherre · commit fce9ba8192b4 · 2020-01-07T17:38:48.000-03:00
Returning a non-NULL time is pointless, sinc a walsender is not a process that would be running normal transactions anyway, but the code was unintentionally exposing the process start time intermittently, which was not only bogus but it also confused monitoring systems looking for idle transactions. Fix by avoiding all updates in walsenders. Backpatch to 11, where walsenders started appearing in pg_stat_activity. Reported-by: Tomas Vondra Discussion: https://postgr.es/m/20191209234409.exe7osmyalwkt5j4@development
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
@@ -817,6 +817,13 @@ 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
