v2-0001-Use-WALReadFromBuffers-in-more-places.patch

From 6902b207cf7497396493aef369a9e275900a86e7 Mon Sep 17 00:00:00 2001
From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Wed, 12 Jun 2024 14:46:16 +0000
Subject: [PATCH v2 1/2] Use WALReadFromBuffers in more places

Commit 91f2cae introduced WALReadFromBuffers, and used it only for
physical replication walsenders. There are couple of other callers
that use read_local_xlog_page page_read callback and logical
replication walsenders can also benefit reading WAL from WAL
buffers using the new function. This commit uses the new function
for these callers.

Author: Bharath Rupireddy
Reviewed-by: Jingtang Zhang, Nitin Jadhav
Discussion: https://www.postgresql.org/message-id/CALj2ACVfF2Uj9NoFy-5m98HNtjHpuD17EDE9twVeJng-jTAe7A%40mail.gmail.com
---
 src/backend/access/transam/xlogutils.c | 10 +++++++++-
 src/backend/replication/walsender.c    | 13 ++++++++++---
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 5295b85fe0..24a7ef0479 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -892,6 +892,7 @@ read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
 	int			count;
 	WALReadError errinfo;
 	TimeLineID	currTLI;
+	Size		rbytes;
 
 	loc = targetPagePtr + reqLen;
 
@@ -1004,7 +1005,14 @@ read_local_xlog_page_guts(XLogReaderState *state, XLogRecPtr targetPagePtr,
 		count = read_upto - targetPagePtr;
 	}
 
-	if (!WALRead(state, cur_page, targetPagePtr, count, tli,
+	/* attempt to read WAL from WAL buffers first */
+	rbytes = WALReadFromBuffers(cur_page, targetPagePtr, count, currTLI);
+	cur_page += rbytes;
+	targetPagePtr += rbytes;
+
+	/* now read the remaining WAL from WAL file */
+	if ((count - rbytes) > 0 &&
+		!WALRead(state, cur_page, targetPagePtr, (count - rbytes), tli,
 				 &errinfo))
 		WALReadRaiseError(&errinfo);
 
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index c623b07cf0..bd0decef3d 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -1056,6 +1056,7 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
 	WALReadError errinfo;
 	XLogSegNo	segno;
 	TimeLineID	currTLI;
+	Size		rbytes;
 
 	/*
 	 * Make sure we have enough WAL available before retrieving the current
@@ -1092,11 +1093,17 @@ 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 */
+	rbytes = WALReadFromBuffers(cur_page, targetPagePtr, count, currTLI);
+	cur_page += rbytes;
+	targetPagePtr += rbytes;
+
+	/* now read the remaining WAL from WAL file */
+	if ((count - rbytes) > 0 &&
+		!WALRead(state,
 				 cur_page,
 				 targetPagePtr,
-				 count,
+				 (count - rbytes),
 				 currTLI,		/* Pass the current TLI because only
 								 * WalSndSegmentOpen controls whether new TLI
 								 * is needed. */
-- 
2.34.1