Add-a-way-to-create-read-stream-object-by-using-SMgr.patch

From 38b57ec7e54a54a0c7b0117a0ecaaf68c643e1b0 Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavuz81@gmail.com>
Date: Sun, 7 Apr 2024 20:16:00 +0300
Subject: [PATCH] Add a way to create read stream object by using SMgrRelation

Currently read stream object can be created only by using Relation,
there is no way to create it by using SMgrRelation.

To achieve that, read_stream_begin_impl() function is created and
contents of the read_stream_begin_relation() is moved into this
function.

Both read_stream_begin_relation() and read_stream_begin_sgmr_relation()
calls read_stream_begin_impl() by Relation and SMgrRelation
respectively.
---
 src/include/storage/read_stream.h     |  8 +++
 src/backend/storage/aio/read_stream.c | 74 ++++++++++++++++++++++-----
 2 files changed, 69 insertions(+), 13 deletions(-)

diff --git a/src/include/storage/read_stream.h b/src/include/storage/read_stream.h
index fae09d2b4cc..601a7fcf92b 100644
--- a/src/include/storage/read_stream.h
+++ b/src/include/storage/read_stream.h
@@ -15,6 +15,7 @@
 #define READ_STREAM_H
 
 #include "storage/bufmgr.h"
+#include "storage/smgr.h"
 
 /* Default tuning, reasonable for many users. */
 #define READ_STREAM_DEFAULT 0x00
@@ -56,6 +57,13 @@ extern ReadStream *read_stream_begin_relation(int flags,
 											  ReadStreamBlockNumberCB callback,
 											  void *callback_private_data,
 											  size_t per_buffer_data_size);
+extern ReadStream *read_stream_begin_sgmr_relation(int flags,
+												   BufferAccessStrategy strategy,
+												   SMgrRelation smgr,
+												   ForkNumber forknum,
+												   ReadStreamBlockNumberCB callback,
+												   void *callback_private_data,
+												   size_t per_buffer_data_size);
 extern Buffer read_stream_next_buffer(ReadStream *stream, void **per_buffer_private);
 extern void read_stream_reset(ReadStream *stream);
 extern void read_stream_end(ReadStream *stream);
diff --git a/src/backend/storage/aio/read_stream.c b/src/backend/storage/aio/read_stream.c
index f54dacdd914..a9a3b0de6c9 100644
--- a/src/backend/storage/aio/read_stream.c
+++ b/src/backend/storage/aio/read_stream.c
@@ -406,14 +406,15 @@ read_stream_look_ahead(ReadStream *stream, bool suppress_advice)
  * write extra data for each block into the space provided to it.  It will
  * also receive callback_private_data for its own purposes.
  */
-ReadStream *
-read_stream_begin_relation(int flags,
-						   BufferAccessStrategy strategy,
-						   Relation rel,
-						   ForkNumber forknum,
-						   ReadStreamBlockNumberCB callback,
-						   void *callback_private_data,
-						   size_t per_buffer_data_size)
+static ReadStream *
+read_stream_begin_impl(int flags,
+					   BufferAccessStrategy strategy,
+					   Relation rel,
+					   SMgrRelation smgr,
+					   ForkNumber forknum,
+					   ReadStreamBlockNumberCB callback,
+					   void *callback_private_data,
+					   size_t per_buffer_data_size)
 {
 	ReadStream *stream;
 	size_t		size;
@@ -422,9 +423,6 @@ read_stream_begin_relation(int flags,
 	int			strategy_pin_limit;
 	uint32		max_pinned_buffers;
 	Oid			tablespace_id;
-	SMgrRelation smgr;
-
-	smgr = RelationGetSmgr(rel);
 
 	/*
 	 * Decide how many I/Os we will allow to run at the same time.  That
@@ -434,7 +432,7 @@ read_stream_begin_relation(int flags,
 	 */
 	tablespace_id = smgr->smgr_rlocator.locator.spcOid;
 	if (!OidIsValid(MyDatabaseId) ||
-		IsCatalogRelation(rel) ||
+		(rel && IsCatalogRelation(rel)) ||
 		IsCatalogRelationOid(smgr->smgr_rlocator.locator.relNumber))
 	{
 		/*
@@ -548,7 +546,7 @@ read_stream_begin_relation(int flags,
 	for (int i = 0; i < max_ios; ++i)
 	{
 		stream->ios[i].op.rel = rel;
-		stream->ios[i].op.smgr = RelationGetSmgr(rel);
+		stream->ios[i].op.smgr = smgr;
 		stream->ios[i].op.smgr_persistence = 0;
 		stream->ios[i].op.forknum = forknum;
 		stream->ios[i].op.strategy = strategy;
@@ -557,6 +555,56 @@ read_stream_begin_relation(int flags,
 	return stream;
 }
 
+/*
+ * Create a new read stream for reading a relation.
+ * See read_stream_begin_impl() for the detailed explanation.
+ */
+ReadStream *
+read_stream_begin_relation(int flags,
+						   BufferAccessStrategy strategy,
+						   Relation rel,
+						   ForkNumber forknum,
+						   ReadStreamBlockNumberCB callback,
+						   void *callback_private_data,
+						   size_t per_buffer_data_size)
+{
+	SMgrRelation smgr;
+
+	smgr = RelationGetSmgr(rel);
+
+	return read_stream_begin_impl(flags,
+								  strategy,
+								  rel,
+								  smgr,
+								  forknum,
+								  callback,
+								  callback_private_data,
+								  per_buffer_data_size);
+}
+
+/*
+ * Create a new read stream for reading a SMgr relation.
+ * See read_stream_begin_impl() for the detailed explanation.
+ */
+ReadStream *
+read_stream_begin_sgmr_relation(int flags,
+								BufferAccessStrategy strategy,
+								SMgrRelation smgr,
+								ForkNumber forknum,
+								ReadStreamBlockNumberCB callback,
+								void *callback_private_data,
+								size_t per_buffer_data_size)
+{
+	return read_stream_begin_impl(flags,
+								  strategy,
+								  NULL,
+								  smgr,
+								  forknum,
+								  callback,
+								  callback_private_data,
+								  per_buffer_data_size);
+}
+
 /*
  * Pull one pinned buffer out of a stream.  Each call returns successive
  * blocks in the order specified by the callback.  If per_buffer_data_size was
-- 
2.43.0