v23-0003-Use-WALReadFromBuffers-in-more-places.patch

From ffa3b4e2bc95cdf69ac0feae0bf2ad268a9115b5 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Fri, 16 Feb 2024 06:55:53 +0000
Subject: [PATCH v23 3/5] Use WALReadFromBuffers in more places

---
 src/backend/access/transam/xlogutils.c | 14 +++++++++++++-
 src/backend/replication/walsender.c    | 16 +++++++++++++---
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 945f1f790d..d4872ec170 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -895,6 +895,8 @@ read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
 	int			count;
 	WALReadError errinfo;
 	TimeLineID	currTLI;
+	Size		nbytes;
+	Size		rbytes;
 
 	loc = targetPagePtr + reqLen;
 
@@ -1007,12 +1009,22 @@ read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
 		count = read_upto - targetPagePtr;
 	}
 
+	/* attempt to read WAL from WAL buffers first */
+	nbytes = XLOG_BLCKSZ;
+	rbytes = WALReadFromBuffers(cur_page, targetPagePtr, nbytes, currTLI);
+	cur_page += rbytes;
+	targetPagePtr += rbytes;
+	nbytes -= rbytes;
+
 	/*
+	 * Now read the remaining WAL from WAL file.
+	 *
 	 * Even though we just determined how much of the page can be validly read
 	 * as 'count', read the whole page anyway. It's guaranteed to be
 	 * zero-padded up to the page boundary if it's incomplete.
 	 */
-	if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
+	if (nbytes > 0 &&
+		!WALRead(state, cur_page, targetPagePtr, nbytes, tli,
 				 &errinfo))
 		WALReadRaiseError(&errinfo);
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index e5477c1de1..24687dab28 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1059,6 +1059,8 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 	WALReadError errinfo;
 	XLogSegNo	segno;
 	TimeLineID	currTLI;
+	Size		nbytes;
+	Size		rbytes;
 
 	/*
 	 * Make sure we have enough WAL available before retrieving the current
@@ -1095,11 +1097,19 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 	else
 		count = flushptr - targetPagePtr;	/* part of the page available */
 
-	/* now actually read the data, we know it's there */
-	if (!WALRead(state,
+	/* attempt to read WAL from WAL buffers first */
+	nbytes = XLOG_BLCKSZ;
+	rbytes = WALReadFromBuffers(cur_page, targetPagePtr, nbytes, currTLI);
+	cur_page += rbytes;
+	targetPagePtr += rbytes;
+	nbytes -= rbytes;
+
+	/* now read the remaining WAL from WAL file */
+	if (nbytes > 0 &&
+		!WALRead(state,
 				 cur_page,
 				 targetPagePtr,
-				 XLOG_BLCKSZ,
+				 nbytes,
 				 currTLI,		/* Pass the current TLI because only
 								 * WalSndSegmentOpen controls whether new TLI
 								 * is needed. */
-- 
2.34.1