v3-0001-Fix-OOM-failure-handling-with-pgstats-entry-creat.patch

From 6fe33b6446f1c57ca7570f742f39f844e36a7c23 Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 4 Sep 2025 16:27:51 +0900
Subject: [PATCH v3 1/2] Fix OOM failure handling with pgstats entry creations

---
 src/backend/utils/activity/pgstat.c       |  7 ++++++
 src/backend/utils/activity/pgstat_shmem.c | 27 ++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/src/backend/utils/activity/pgstat.c b/src/backend/utils/activity/pgstat.c
index ffb5b8cce344..8cba6e9cdf8c 100644
--- a/src/backend/utils/activity/pgstat.c
+++ b/src/backend/utils/activity/pgstat.c
@@ -1975,6 +1975,13 @@ pgstat_read_statsfile(void)
 
 					header = pgstat_init_entry(key.kind, p);
 					dshash_release_lock(pgStatLocal.shared_hash, p);
+					if (header == NULL)
+					{
+						elog(WARNING, "could not allocate entry %u/%u/%" PRIu64 " of type %c",
+							 key.kind, key.dboid,
+							 key.objid, t);
+						goto error;
+					}
 
 					if (!read_chunk(fpin,
 									pgstat_get_entry_data(key.kind, header),
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
index 62de34744536..8f8b57e8ee8a 100644
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -289,6 +289,12 @@ pgstat_detach_shmem(void)
  * ------------------------------------------------------------
  */
 
+/*
+ * Initialize entry newly-created.
+ *
+ * Returns NULL in the event of an allocation failure, giving the possibility
+ * for callers to deal with any cleanup actions.
+ */
 PgStatShared_Common *
 pgstat_init_entry(PgStat_Kind kind,
 				  PgStatShared_HashEntry *shhashent)
@@ -311,7 +317,12 @@ pgstat_init_entry(PgStat_Kind kind,
 	pg_atomic_init_u32(&shhashent->generation, 0);
 	shhashent->dropped = false;
 
-	chunk = dsa_allocate0(pgStatLocal.dsa, pgstat_get_kind_info(kind)->shared_size);
+	chunk = dsa_allocate_extended(pgStatLocal.dsa,
+								  pgstat_get_kind_info(kind)->shared_size,
+								  DSA_ALLOC_ZERO | DSA_ALLOC_NO_OOM);
+	if (chunk == InvalidDsaPointer)
+		return NULL;
+
 	shheader = dsa_get_address(pgStatLocal.dsa, chunk);
 	shheader->magic = 0xdeadbeef;
 
@@ -509,6 +520,20 @@ pgstat_get_entry_ref(PgStat_Kind kind, Oid dboid, uint64 objid, bool create,
 		if (!shfound)
 		{
 			shheader = pgstat_init_entry(kind, shhashent);
+			if (shheader == NULL)
+			{
+				/*
+				 * Failed the allocation of a new entry, so clean up the shared
+				 * hashtable before giving up.
+				 */
+				dshash_delete_entry(pgStatLocal.shared_hash, shhashent);
+
+				ereport(ERROR,
+						(errcode(ERRCODE_OUT_OF_MEMORY),
+						 errmsg("out of memory"),
+						 errdetail("Failed while allocating entry %u/%u/%" PRIu64 " of kind %u.",
+								   key.kind, key.dboid, key.objid, kind)));
+			}
 			pgstat_acquire_entry_ref(entry_ref, shhashent, shheader);
 
 			if (created_entry != NULL)
-- 
2.51.0