0002-Add-various-logs-in-pgstats-to-debug-entry-handling.patch

From 30fe57ed7fd72f86f233edd9bab0fd8c20099dba Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Thu, 5 Dec 2024 13:25:35 +0900
Subject: [PATCH 2/2] Add various logs in pgstats to debug entry handling

Not for commit, nice to play with.
---
 src/backend/utils/activity/pgstat_replslot.c |  1 +
 src/backend/utils/activity/pgstat_shmem.c    | 37 ++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/src/backend/utils/activity/pgstat_replslot.c b/src/backend/utils/activity/pgstat_replslot.c
index ddf2ab9928..e41806d7f6 100644
--- a/src/backend/utils/activity/pgstat_replslot.c
+++ b/src/backend/utils/activity/pgstat_replslot.c
@@ -157,6 +157,7 @@ pgstat_drop_replslot(ReplicationSlot *slot)
 {
 	Assert(LWLockHeldByMeInMode(ReplicationSlotAllocationLock, LW_EXCLUSIVE));
 
+	elog(WARNING, "XXX pgstat_drop_replslot index %d", ReplicationSlotIndex(slot));
 	if (!pgstat_drop_entry(PGSTAT_KIND_REPLSLOT, InvalidOid,
 						   ReplicationSlotIndex(slot)))
 		pgstat_request_entry_refs_gc();
diff --git a/src/backend/utils/activity/pgstat_shmem.c b/src/backend/utils/activity/pgstat_shmem.c
index ccb5e5f6de..f717b52226 100644
--- a/src/backend/utils/activity/pgstat_shmem.c
+++ b/src/backend/utils/activity/pgstat_shmem.c
@@ -296,6 +296,7 @@ pgstat_init_entry(PgStat_Kind kind,
 	/* Create new stats entry. */
 	dsa_pointer chunk;
 	PgStatShared_Common *shheader;
+	PgStat_HashKey key = shhashent->key;
 
 	/*
 	 * Initialize refcount to 1, marking it as valid / not dropped. The entry
@@ -310,6 +311,8 @@ pgstat_init_entry(PgStat_Kind kind,
 	 */
 	pg_atomic_init_u32(&shhashent->generation, 0);
 	shhashent->dropped = false;
+	elog(WARNING, "XXX key %u/%u/%llu pgstat_init_entry generation 0",
+		 key.kind, key.dboid, (unsigned long long) key.objid);
 
 	chunk = dsa_allocate0(pgStatLocal.dsa, pgstat_get_kind_info(kind)->shared_size);
 	shheader = dsa_get_address(pgStatLocal.dsa, chunk);
@@ -327,6 +330,7 @@ static PgStatShared_Common *
 pgstat_reinit_entry(PgStat_Kind kind, PgStatShared_HashEntry *shhashent)
 {
 	PgStatShared_Common *shheader;
+	PgStat_HashKey key = shhashent->key;
 
 	shheader = dsa_get_address(pgStatLocal.dsa, shhashent->body);
 
@@ -339,6 +343,8 @@ pgstat_reinit_entry(PgStat_Kind kind, PgStatShared_HashEntry *shhashent)
 	 */
 	pg_atomic_fetch_add_u32(&shhashent->generation, 1);
 	shhashent->dropped = false;
+	elog(WARNING, "XXX key %u/%u/%llu pgstat_reinit_entry generation++ refcount++",
+		 key.kind, key.dboid, (unsigned long long) key.objid);
 
 	/* reinitialize content */
 	Assert(shheader->magic == 0xdeadbeef);
@@ -369,10 +375,13 @@ pgstat_acquire_entry_ref(PgStat_EntryRef *entry_ref,
 						 PgStatShared_HashEntry *shhashent,
 						 PgStatShared_Common *shheader)
 {
+	PgStat_HashKey key = shhashent->key;
 	Assert(shheader->magic == 0xdeadbeef);
 	Assert(pg_atomic_read_u32(&shhashent->refcount) > 0);
 
 	pg_atomic_fetch_add_u32(&shhashent->refcount, 1);
+	elog(WARNING, "XXX key %u/%u/%llu pgstat_acquire_entry_ref refcount++",
+		 key.kind, key.dboid, (unsigned long long) key.objid);
 
 	dshash_release_lock(pgStatLocal.shared_hash, shhashent);
 
@@ -594,6 +603,9 @@ pgstat_release_entry_ref(PgStat_HashKey key, PgStat_EntryRef *entry_ref,
 		 * increasing the refcount because it is not "legal" to create
 		 * additional references to dropped entries.
 		 */
+		elog(WARNING,
+			 "XXX: key %u/%u/%llu pgstat_release_entry_ref refcount--",
+			 key.kind, key.dboid, (unsigned long long) key.objid);
 		if (pg_atomic_fetch_sub_u32(&entry_ref->shared_entry->refcount, 1) == 1)
 		{
 			PgStatShared_HashEntry *shent;
@@ -620,6 +632,9 @@ pgstat_release_entry_ref(PgStat_HashKey key, PgStat_EntryRef *entry_ref,
 			if (pg_atomic_read_u32(&entry_ref->shared_entry->generation) ==
 				entry_ref->generation)
 			{
+				elog(WARNING,
+					 "XXX: key %u/%u/%llu pgstat_release_entry_ref same generation",
+					 key.kind, key.dboid, (unsigned long long) key.objid);
 				/* Same "generation", so we're OK with the removal */
 				Assert(pg_atomic_read_u32(&entry_ref->shared_entry->refcount) == 0);
 				Assert(entry_ref->shared_entry == shent);
@@ -627,6 +642,12 @@ pgstat_release_entry_ref(PgStat_HashKey key, PgStat_EntryRef *entry_ref,
 			}
 			else
 			{
+				elog(WARNING, "XXX: key %u/%u/%llu pgstat_release_entry_ref different generation "
+					 "shared_ref=%u entry_ref=%u",
+					 key.kind, key.dboid, (unsigned long long) key.objid,
+					 pg_atomic_read_u32(&entry_ref->shared_entry->generation),
+					 entry_ref->generation);
+
 				/*
 				 * Shared stats entry has been reinitialized, so do not drop
 				 * its shared entry, only release its lock.
@@ -753,6 +774,14 @@ pgstat_gc_entry_refs(void)
 		if (entry_ref->pending != NULL)
 			continue;
 
+		if (entry_ref->shared_entry->key.kind == PGSTAT_KIND_REPLSLOT)
+		{
+			PgStat_HashKey key = entry_ref->shared_entry->key;
+			elog(WARNING, "XXX key %u/%u/%llu pgstat_gc_entry_refs dropped generation=%d",
+				 key.kind, key.dboid, (unsigned long long) key.objid,
+				 entry_ref->generation);
+		}
+
 		pgstat_release_entry_ref(ent->key, entry_ref, false);
 	}
 
@@ -852,6 +881,7 @@ static bool
 pgstat_drop_entry_internal(PgStatShared_HashEntry *shent,
 						   dshash_seq_status *hstat)
 {
+	PgStat_HashKey key = shent->key;
 	Assert(shent->body != InvalidDsaPointer);
 
 	/* should already have released local reference */
@@ -874,11 +904,15 @@ pgstat_drop_entry_internal(PgStatShared_HashEntry *shent,
 	/* release refcount marking entry as not dropped */
 	if (pg_atomic_sub_fetch_u32(&shent->refcount, 1) == 0)
 	{
+		elog(WARNING, "XXX key %u/%u/%llu pgstat_drop_entry_internal refcount=0",
+			 key.kind, key.dboid, (unsigned long long) key.objid);
 		pgstat_free_entry(shent, hstat);
 		return true;
 	}
 	else
 	{
+		elog(WARNING, "XXX key %u/%u/%llu pgstat_drop_entry_internal refcount>0",
+			 key.kind, key.dboid, (unsigned long long) key.objid);
 		if (!hstat)
 			dshash_release_lock(pgStatLocal.shared_hash, shent);
 		return false;
@@ -963,6 +997,9 @@ pgstat_drop_entry(PgStat_Kind kind, Oid dboid, uint64 objid)
 	key.dboid = dboid;
 	key.objid = objid;
 
+	elog(WARNING, "XXX key %u/%u/%llu pgstat_drop_entry",
+		 key.kind, key.dboid, (unsigned long long) key.objid);
+
 	/* delete local reference */
 	if (pgStatEntryRefHash)
 	{
-- 
2.45.2