Improve check for detection of pending data in backend statistics

michaelpq · michaelpq · commit 9a8dd2c5a6d9 · 2025-03-08T10:56:30.000+09:00
The callback pgstat_backend_have_pending_cb() is used as a way for pg_stat_report() to detect if there is any pending data for backend statistics. It did not include a check based on pgstat_tracks_backend_bktype(), that discards processes whose backend types do not support backend statistics. The logic is not a problem on HEAD, as processes that do not support backend statistics cannot touch PendingBackendStats, so the callback would always report that there is no pending data in this case. However, we would run into trouble once backend statistics include portions of pending stats that are not always zeroed, like pgWalUsage. There is no reason for pgstat_backend_have_pending_cb() to not check for pgstat_tracks_backend_bktype(), anyway, and this pattern is safer in the long run, so let's update the code to do so. While on it, this commit adds a proper initialization to PendingBackendStats. Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Co-authored-by: Michael Paquier <michael@paquier.xyz> Discussion: https://postgr.es/m/Z8l6EMM4ImVoWRkg@ip-10-97-1-34.eu-west-3.compute.internal
diff --git a/src/backend/utils/activity/pgstat_backend.c b/src/backend/utils/activity/pgstat_backend.c
@@ -36,7 +36,7 @@
  * reported within critical sections so we use static memory in order to avoid
  * memory allocation.
  */
-static PgStat_BackendPending PendingBackendStats;
+static PgStat_BackendPending PendingBackendStats = {0};
 
 /*
  * Utility routines to report I/O stats for backends, kept here to avoid
@@ -222,6 +222,9 @@ pgstat_flush_backend(bool nowait, bits32 flags)
 bool
 pgstat_backend_have_pending_cb(void)
 {
+	if (!pgstat_tracks_backend_bktype(MyBackendType))
+		return false;
+
 	return (!pg_memory_is_all_zeros(&PendingBackendStats,
 									sizeof(struct PgStat_BackendPending)));
 }
