From e7ec4f3af86499b8433379b3b102eb58f75cf361 Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Fri, 9 Aug 2024 11:41:52 +0300
Subject: [PATCH v2 1/2] Use read stream in pg_visibility in
 collect_visibility_data()

Instead of reading blocks with ReadBufferExtended() in
collect_visibility_data(), use read stream.

This change provides about 4% performance improvement.
---
 contrib/pg_visibility/pg_visibility.c | 53 ++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/contrib/pg_visibility/pg_visibility.c b/contrib/pg_visibility/pg_visibility.c
index 773ba92e454..ece67ccbe5f 100644
--- a/contrib/pg_visibility/pg_visibility.c
+++ b/contrib/pg_visibility/pg_visibility.c
@@ -21,6 +21,7 @@
 #include "storage/bufmgr.h"
 #include "storage/proc.h"
 #include "storage/procarray.h"
+#include "storage/read_stream.h"
 #include "storage/smgr.h"
 #include "utils/rel.h"
 #include "utils/snapmgr.h"
@@ -41,6 +42,16 @@ typedef struct corrupt_items
 	ItemPointer tids;
 } corrupt_items;
 
+/*
+ * Helper struct for read stream object used in
+ * collect_visibility_data() function.
+ */
+struct collect_visibility_data_read_stream_private
+{
+	BlockNumber blocknum;
+	BlockNumber nblocks;
+};
+
 PG_FUNCTION_INFO_V1(pg_visibility_map);
 PG_FUNCTION_INFO_V1(pg_visibility_map_rel);
 PG_FUNCTION_INFO_V1(pg_visibility);
@@ -463,6 +474,23 @@ pg_visibility_tupdesc(bool include_blkno, bool include_pd)
 	return BlessTupleDesc(tupdesc);
 }
 
+/*
+ * Callback function to get next block for read stream object used in
+ * collect_visibility_data() function.
+ */
+static BlockNumber
+collect_visibility_data_read_stream_next_block(ReadStream *stream,
+											   void *callback_private_data,
+											   void *per_buffer_data)
+{
+	struct collect_visibility_data_read_stream_private *p = callback_private_data;
+
+	if (p->blocknum < p->nblocks)
+		return p->blocknum++;
+
+	return InvalidBlockNumber;
+}
+
 /*
  * Collect visibility data about a relation.
  *
@@ -478,6 +506,8 @@ collect_visibility_data(Oid relid, bool include_pd)
 	BlockNumber blkno;
 	Buffer		vmbuffer = InvalidBuffer;
 	BufferAccessStrategy bstrategy = GetAccessStrategy(BAS_BULKREAD);
+	struct collect_visibility_data_read_stream_private p;
+	ReadStream *stream = NULL;
 
 	rel = relation_open(relid, AccessShareLock);
 
@@ -489,6 +519,20 @@ collect_visibility_data(Oid relid, bool include_pd)
 	info->next = 0;
 	info->count = nblocks;
 
+	/* Crate a read stream if read will be done. */
+	if (include_pd)
+	{
+		p.blocknum = 0;
+		p.nblocks = nblocks;
+		stream = read_stream_begin_relation(READ_STREAM_FULL,
+											bstrategy,
+											rel,
+											MAIN_FORKNUM,
+											collect_visibility_data_read_stream_next_block,
+											&p,
+											0);
+	}
+
 	for (blkno = 0; blkno < nblocks; ++blkno)
 	{
 		int32		mapbits;
@@ -513,8 +557,7 @@ collect_visibility_data(Oid relid, bool include_pd)
 			Buffer		buffer;
 			Page		page;
 
-			buffer = ReadBufferExtended(rel, MAIN_FORKNUM, blkno, RBM_NORMAL,
-										bstrategy);
+			buffer = read_stream_next_buffer(stream, NULL);
 			LockBuffer(buffer, BUFFER_LOCK_SHARE);
 
 			page = BufferGetPage(buffer);
@@ -525,6 +568,12 @@ collect_visibility_data(Oid relid, bool include_pd)
 		}
 	}
 
+	if (include_pd && stream)
+	{
+		Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+		read_stream_end(stream);
+	}
+
 	/* Clean up. */
 	if (vmbuffer != InvalidBuffer)
 		ReleaseBuffer(vmbuffer);
-- 
2.45.2