From 213f0079b3415ad8f5f0a62d119ed1f0a448ad8f Mon Sep 17 00:00:00 2001
From: Michael Paquier <michael@paquier.xyz>
Date: Fri, 13 Mar 2026 10:48:45 +0900
Subject: [PATCH] pgstattuple: Optimize btree and hash index functions with
 streaming read

This commit replaces the synchronous ReadBufferExtended() loops with the
streaming read routines, affecting pgstatindex() (for btree) and
pgstathashindex() (for hash indexes).

Under test conditions similar to 6c228755add8 (some dm_delay and
debug_io_direct=data), this can result in nice runtime and IO gains.

Author: Xuneng Zhou <xunengzhou@gmail.com>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Discussion: https://postgr.es/m/CABPTF7VrqfbcDXqGrdLQ2xaQ=K0RzExNuw6U_GGqzSJu32wfdQ@mail.gmail.com
---
 contrib/pgstattuple/pgstatindex.c | 66 +++++++++++++++++++++++++------
 1 file changed, 55 insertions(+), 11 deletions(-)

diff --git a/contrib/pgstattuple/pgstatindex.c b/contrib/pgstattuple/pgstatindex.c
index ef723af1f19..3a3f2637bd9 100644
--- a/contrib/pgstattuple/pgstatindex.c
+++ b/contrib/pgstattuple/pgstatindex.c
@@ -37,6 +37,7 @@
 #include "funcapi.h"
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
+#include "storage/read_stream.h"
 #include "utils/rel.h"
 #include "utils/varlena.h"
 
@@ -217,6 +218,9 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 	BlockNumber blkno;
 	BTIndexStat indexStat;
 	BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
+	BlockRangeReadStreamPrivate p;
+	ReadStream *stream;
+	BlockNumber startblk;
 
 	if (!IS_INDEX(rel) || !IS_BTREE(rel))
 		ereport(ERROR,
@@ -273,11 +277,28 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 	indexStat.fragments = 0;
 
 	/*
-	 * Scan all blocks except the metapage
+	 * Scan all blocks except the metapage (0th page) using streaming reads
 	 */
 	nblocks = RelationGetNumberOfBlocks(rel);
+	startblk = BTREE_METAPAGE + 1;
 
-	for (blkno = 1; blkno < nblocks; blkno++)
+	p.current_blocknum = startblk;
+	p.last_exclusive = nblocks;
+
+	/*
+	 * It is safe to use batchmode as block_range_read_stream_cb takes no
+	 * locks.
+	 */
+	stream = read_stream_begin_relation(READ_STREAM_FULL |
+										READ_STREAM_USE_BATCHING,
+										bstrategy,
+										rel,
+										MAIN_FORKNUM,
+										block_range_read_stream_cb,
+										&p,
+										0);
+
+	for (blkno = startblk; blkno < nblocks; blkno++)
 	{
 		Buffer		buffer;
 		Page		page;
@@ -285,8 +306,7 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 
 		CHECK_FOR_INTERRUPTS();
 
-		/* Read and lock buffer */
-		buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL, bstrategy);
+		buffer = read_stream_next_buffer(stream, NULL);
 		LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
 		page = BufferGetPage(buffer);
@@ -322,11 +342,12 @@ pgstatindex_impl(Relation rel, FunctionCallInfo fcinfo)
 		else
 			indexStat.internal_pages++;
 
-		/* Unlock and release buffer */
-		LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
-		ReleaseBuffer(buffer);
+		UnlockReleaseBuffer(buffer);
 	}
 
+	Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+	read_stream_end(stream);
+
 	relation_close(rel, AccessShareLock);
 
 	/*----------------------------
@@ -600,6 +621,9 @@ pgstathashindex(PG_FUNCTION_ARGS)
 	HashMetaPage metap;
 	float8		free_percent;
 	uint64		total_space;
+	BlockRangeReadStreamPrivate p;
+	ReadStream *stream;
+	BlockNumber startblk;
 
 	/*
 	 * This uses relation_open() and not index_open().  The latter allows
@@ -644,16 +668,33 @@ pgstathashindex(PG_FUNCTION_ARGS)
 	/* prepare access strategy for this index */
 	bstrategy = GetAccessStrategy(BAS_BULKREAD);
 
-	/* Start from blkno 1 as 0th block is metapage */
-	for (blkno = 1; blkno < nblocks; blkno++)
+	/* Scan all blocks except the metapage (0th page) using streaming reads */
+	startblk = HASH_METAPAGE + 1;
+
+	p.current_blocknum = startblk;
+	p.last_exclusive = nblocks;
+
+	/*
+	 * It is safe to use batchmode as block_range_read_stream_cb takes no
+	 * locks.
+	 */
+	stream = read_stream_begin_relation(READ_STREAM_FULL |
+										READ_STREAM_USE_BATCHING,
+										bstrategy,
+										rel,
+										MAIN_FORKNUM,
+										block_range_read_stream_cb,
+										&p,
+										0);
+
+	for (blkno = startblk; blkno < nblocks; blkno++)
 	{
 		Buffer		buf;
 		Page		page;
 
 		CHECK_FOR_INTERRUPTS();
 
-		buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
-								 bstrategy);
+		buf = read_stream_next_buffer(stream, NULL);
 		LockBuffer(buf, BUFFER_LOCK_SHARE);
 		page = BufferGetPage(buf);
 
@@ -698,6 +739,9 @@ pgstathashindex(PG_FUNCTION_ARGS)
 		UnlockReleaseBuffer(buf);
 	}
 
+	Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+	read_stream_end(stream);
+
 	/* Done accessing the index */
 	relation_close(rel, AccessShareLock);