From 1c24af4fedb372b9b89d0635895860889da86b47 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Wed, 19 Nov 2025 15:32:20 -0500
Subject: [PATCH v6 13/14] WIP: Make UnlockReleaseBuffer() more efficient

Now that the buffer content lock is implemented as part of BufferDesc.state,
releasing the lock and unpinning the buffer can be implemented as a single
atomic operation.

Author:
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:
---
 src/backend/access/nbtree/nbtpage.c | 22 +++++++++++-
 src/backend/storage/buffer/bufmgr.c | 52 ++++++++++++++++++++++++++++-
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/src/backend/access/nbtree/nbtpage.c b/src/backend/access/nbtree/nbtpage.c
index 30b43a4dd18..2fd8141854c 100644
--- a/src/backend/access/nbtree/nbtpage.c
+++ b/src/backend/access/nbtree/nbtpage.c
@@ -1006,11 +1006,18 @@ _bt_relandgetbuf(Relation rel, Buffer obuf, BlockNumber blkno, int access)
 
 	Assert(BlockNumberIsValid(blkno));
 	if (BufferIsValid(obuf))
+	{
+		_bt_relbuf(rel, obuf);
+#if 0
+		Assert(BufferGetBlockNumber(obuf) != blkno);
 		_bt_unlockbuf(rel, obuf);
-	buf = ReleaseAndReadBuffer(obuf, rel, blkno);
+#endif
+	}
+	buf = ReadBuffer(rel, blkno);
 	_bt_lockbuf(rel, buf, access);
 
 	_bt_checkpage(rel, buf);
+
 	return buf;
 }
 
@@ -1022,8 +1029,21 @@ _bt_relandgetbuf(Relation rel, Buffer obuf, BlockNumber blkno, int access)
 void
 _bt_relbuf(Relation rel, Buffer buf)
 {
+#if 0
 	_bt_unlockbuf(rel, buf);
 	ReleaseBuffer(buf);
+#else
+	/*
+	 * Buffer is pinned and locked, which means that it is expected to be
+	 * defined and addressable.  Check that proactively.
+	 */
+	VALGRIND_CHECK_MEM_IS_DEFINED(BufferGetPage(buf), BLCKSZ);
+
+	UnlockReleaseBuffer(buf);
+
+	if (!RelationUsesLocalBuffers(rel))
+		VALGRIND_MAKE_MEM_NOACCESS(BufferGetPage(buf), BLCKSZ);
+#endif
 }
 
 /*
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 9ed7a368d74..584c3b2ee75 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -5437,13 +5437,63 @@ ReleaseBuffer(Buffer buffer)
 /*
  * UnlockReleaseBuffer -- release the content lock and pin on a buffer
  *
- * This is just a shorthand for a common combination.
+ * This is just a, more efficient, shorthand for a common combination.
  */
 void
 UnlockReleaseBuffer(Buffer buffer)
 {
+#if 1
+	int			mode;
+	BufferDesc *buf;
+	PrivateRefCountEntry *ref;
+	uint64		sub;
+	uint64		lockstate;
+
+	if (!BufferIsValid(buffer))
+		elog(ERROR, "bad buffer ID: %d", buffer);
+
+	if (BufferIsLocal(buffer))
+	{
+		UnpinLocalBuffer(buffer);
+		return;
+	}
+
+	ResourceOwnerForgetBuffer(CurrentResourceOwner, buffer);
+
+	buf = GetBufferDescriptor(buffer - 1);
+
+	mode = BufferLockDisownInternal(buffer, buf);
+
+	/* compute state modification for lock release */
+	sub = BufferLockReleaseSub(mode);
+
+	/* compute state modification for pin release */
+	ref = GetPrivateRefCountEntry(buffer, false);
+	Assert(ref != NULL);
+	Assert(ref->data.refcount > 0);
+	ref->data.refcount--;
+
+	if (ref->data.refcount == 0)
+	{
+		sub |= BUF_REFCOUNT_ONE;
+		ForgetPrivateRefCountEntry(ref);
+	}
+
+	/* perform the lock and pin release in one atomic op */
+	lockstate = pg_atomic_sub_fetch_u64(&buf->state, sub);
+
+	/* wake up waiters etc */
+	BufferLockProcessRelease(buf, mode, lockstate);
+
+	if (lockstate & BM_PIN_COUNT_WAITER)
+		WakePinCountWaiter(buf);
+
+	RESUME_INTERRUPTS();
+
+#else
 	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 	ReleaseBuffer(buffer);
+#endif
 }
 
 /*
-- 
2.48.1.76.g4e746b1a31.dirty