From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 24 Aug 2023 07:58:01 -0700
Subject: [PATCH v2 2/2] fix pg_stat_get_backend_subxact to use real backend id

---
 src/backend/utils/activity/backend_status.c | 36 +++++++++++++++------
 src/backend/utils/adt/pgstatfuncs.c         |  2 +-
 src/include/utils/backend_status.h          |  1 +
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/src/backend/utils/activity/backend_status.c b/src/backend/utils/activity/backend_status.c
index aea05a9014..d5babd9fb0 100644
--- a/src/backend/utils/activity/backend_status.c
+++ b/src/backend/utils/activity/backend_status.c
@@ -1088,9 +1088,33 @@ cmp_lbestatus(const void *a, const void *b)
  */
 PgBackendStatus *
 pgstat_get_beentry_by_backend_id(BackendId beid)
+{
+	LocalPgBackendStatus *ret = pgstat_get_local_beentry_by_backend_id(beid);
+
+	if (ret)
+		return &ret->backendStatus;
+
+	return NULL;
+}
+
+
+/* ----------
+ * pgstat_get_local_beentry_by_backend_id() -
+ *
+ *	Like pgstat_get_beentry_by_backend_id() but with locally computed additions
+ *	(like xid and xmin values of the backend)
+ *
+ *	The beid argument is the BackendId of the desired session
+ *	(note that this is unlike pgstat_get_local_beentry_by_index()).
+ *
+ *	NB: caller is responsible for checking if the user is permitted to see this
+ *	info (especially the querystring).
+ * ----------
+ */
+LocalPgBackendStatus *
+pgstat_get_local_beentry_by_backend_id(BackendId beid)
 {
 	LocalPgBackendStatus key;
-	LocalPgBackendStatus *ret;
 
 	pgstat_read_current_status();
 
@@ -1099,14 +1123,8 @@ pgstat_get_beentry_by_backend_id(BackendId beid)
 	 * bsearch() to search it efficiently.
 	 */
 	key.backend_id = beid;
-	ret = (LocalPgBackendStatus *) bsearch(&key, localBackendStatusTable,
-										   localNumBackends,
-										   sizeof(LocalPgBackendStatus),
-										   cmp_lbestatus);
-	if (ret)
-		return &ret->backendStatus;
-
-	return NULL;
+	return bsearch(&key, localBackendStatusTable, localNumBackends,
+				   sizeof(LocalPgBackendStatus), cmp_lbestatus);
 }
 
 
diff --git a/src/backend/utils/adt/pgstatfuncs.c b/src/backend/utils/adt/pgstatfuncs.c
index 7deefed5ab..62d327bb92 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_get_local_beentry_by_index(beid)) != NULL)
+	if ((local_beentry = pgstat_get_local_beentry_by_backend_id(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 e53098ec9e..a996c7fd23 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_get_beentry_by_backend_id(BackendId beid);
+extern LocalPgBackendStatus *pgstat_get_local_beentry_by_backend_id(BackendId beid);
 extern LocalPgBackendStatus *pgstat_get_local_beentry_by_index(int beid);
 extern char *pgstat_clip_activity(const char *raw_activity);
 
-- 
2.25.1


--gKMricLos+KVdGMg--