commit d4292d3347658f61855fd84827954f587838a324
Author: Ian Barwick <barwick@gmail.com>
Date:   Thu Aug 24 10:16:51 2023 +0900

    pg_stat_get_backend_subxact(): handle backend ID correctly

diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index 38f91a495b..bce7836264 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -1136,6 +1136,39 @@ pgstat_fetch_stat_local_beentry(int beid)
 }
 
 
+/* ----------
+ * pgstat_fetch_stat_backend_local_beentry() -
+ *
+ *	Like pgstat_fetch_stat_local_beentry() but takes the BackendId of the
+ *  desired session.
+ *
+ *	Returns NULL if the given beid doesn't identify any known session.
+ *
+ *	NB: caller is responsible for a check if the user is permitted to see
+ *	this info (especially the querystring).
+ * ----------
+ */
+
+LocalPgBackendStatus *
+pgstat_fetch_stat_backend_local_beentry(BackendId beid)
+{
+	LocalPgBackendStatus key;
+
+	pgstat_read_current_status();
+
+	/*
+	 * Since the localBackendStatusTable is in order by backend_id, we can use
+	 * bsearch() to search it efficiently.
+	 */
+	key.backend_id = beid;
+
+	return (LocalPgBackendStatus *) bsearch(&key, localBackendStatusTable,
+											localNumBackends,
+											sizeof(LocalPgBackendStatus),
+											cmp_lbestatus);
+}
+
+
 /* ----------
  * pgstat_fetch_stat_numbackends() -
  *
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 2b9742ad21..8479ea130b 100644
--- a/src/backend/utils/adt/pgstatfuncs.c
+++ b/src/backend/utils/adt/pgstatfuncs.c
@@ -727,7 +727,7 @@ pg_stat_get_backend_subxact(PG_FUNCTION_ARGS)
 
 	BlessTupleDesc(tupdesc);
 
-	if ((local_beentry = pgstat_fetch_stat_local_beentry(beid)) != NULL)
+	if ((local_beentry = pgstat_fetch_stat_backend_local_beentry(beid)) != NULL)
 	{
 		/* Fill values and NULLs */
 		values[0] = Int32GetDatum(local_beentry->backend_subxact_count);
diff --git a/src/include/utils/backend_status.h b/src/include/utils/backend_status.h
index 77939a0aed..760ddc48ae 100644
--- a/src/include/utils/backend_status.h
+++ b/src/include/utils/backend_status.h
@@ -334,6 +334,7 @@ extern uint64 pgstat_get_my_query_id(void);
  */
 extern int	pgstat_fetch_stat_numbackends(void);
 extern PgBackendStatus *pgstat_fetch_stat_beentry(BackendId beid);
+extern LocalPgBackendStatus *pgstat_fetch_stat_backend_local_beentry(BackendId beid);
 extern LocalPgBackendStatus *pgstat_fetch_stat_local_beentry(int beid);
 extern char *pgstat_clip_activity(const char *raw_activity);