From: Masahiko Sawada <msawada@postgresql.org>
Date: Fri, 29 Aug 2025 00:06:44 +0000 (-0700)
Subject: Use LW_SHARED in walsummarizer.c for WALSummarizerLock lock where possible.
X-Git-Tag: REL_18_RC1~11
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=514688656b8bca623bd2d1a28a549f8a56751612;p=thirdparty%2Fpostgresql.git

Use LW_SHARED in walsummarizer.c for WALSummarizerLock lock where possible.

Previously, we used LW_EXCLUSIVE in several places despite only reading
WalSummarizerCtl fields. This patch reduces the lock level to LW_SHARED
where we are only reading the shared fields.

Backpatch to 17, where wal summarization was introduced.

Reviewed-by: Nathan Bossart <nathandbossart@gmail.com>
Discussion: https://postgr.es/m/CAD21AoDdKhf_9oriEYxY-JCdF+Oe_muhca3pcdkMEdBMzyHyKw@mail.gmail.com
Backpatch-through: 17
---

diff --git a/src/backend/postmaster/walsummarizer.c b/src/backend/postmaster/walsummarizer.c
index 0fec4f1f871..11857356ce4 100644
--- a/src/backend/postmaster/walsummarizer.c
+++ b/src/backend/postmaster/walsummarizer.c
@@ -644,7 +644,7 @@ WakeupWalSummarizer(void)
 	if (WalSummarizerCtl == NULL)
 		return;
 
-	LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
+	LWLockAcquire(WALSummarizerLock, LW_SHARED);
 	pgprocno = WalSummarizerCtl->summarizer_pgprocno;
 	LWLockRelease(WALSummarizerLock);
 
@@ -685,7 +685,7 @@ WaitForWalSummarization(XLogRecPtr lsn)
 		/*
 		 * If the LSN summarized on disk has reached the target value, stop.
 		 */
-		LWLockAcquire(WALSummarizerLock, LW_EXCLUSIVE);
+		LWLockAcquire(WALSummarizerLock, LW_SHARED);
 		summarized_lsn = WalSummarizerCtl->summarized_lsn;
 		pending_lsn = WalSummarizerCtl->pending_lsn;
 		LWLockRelease(WALSummarizerLock);