From 7fde68340b0a0b80e4e6d2de5c1771a4cd5c7bfe Mon Sep 17 00:00:00 2001
From: Melanie Plageman <melanieplageman@gmail.com>
Date: Tue, 1 Apr 2025 18:07:38 -0400
Subject: [PATCH v12 3/3] Use streaming read I/O in autoprewarm

Make a read stream for each valid fork of each valid relation
represented in the autoprewarm dump file and prewarm those blocks
through the read stream API instead of by directly invoking
ReadBuffer().

Co-authored-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Co-authored-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/flat/CAN55FZ3n8Gd%2BhajbL%3D5UkGzu_aHGRqnn%2BxktXq2fuds%3D1AOR6Q%40mail.gmail.com
---
 contrib/pg_prewarm/autoprewarm.c | 127 +++++++++++++++++++++++++------
 src/tools/pgindent/typedefs.list |   1 +
 2 files changed, 105 insertions(+), 23 deletions(-)

diff --git a/contrib/pg_prewarm/autoprewarm.c b/contrib/pg_prewarm/autoprewarm.c
index fe79c8c71bf..4b35a19eec1 100644
--- a/contrib/pg_prewarm/autoprewarm.c
+++ b/contrib/pg_prewarm/autoprewarm.c
@@ -41,6 +41,7 @@
 #include "storage/latch.h"
 #include "storage/lwlock.h"
 #include "storage/procsignal.h"
+#include "storage/read_stream.h"
 #include "storage/smgr.h"
 #include "tcop/tcopprot.h"
 #include "utils/guc.h"
@@ -75,6 +76,28 @@ typedef struct AutoPrewarmSharedState
 	int			prewarmed_blocks;
 } AutoPrewarmSharedState;
 
+/*
+ * Private data passed through the read stream API for our use in the
+ * callback.
+ */
+typedef struct AutoPrewarmReadStreamData
+{
+	/* The array of records containing the blocks we should prewarm. */
+	BlockInfoRecord *block_info;
+
+	/*
+	 * `pos` is the read stream callback's index into block_info. Because the
+	 * read stream may read ahead, pos is likely to be ahead of the index in
+	 * the main loop in autoprewarm_database_main().
+	 */
+	int			pos;
+	Oid			database;
+	RelFileNumber filenumber;
+	ForkNumber	forknum;
+	BlockNumber nblocks;
+} AutoPrewarmReadStreamData;
+
+
 PGDLLEXPORT void autoprewarm_main(Datum main_arg);
 PGDLLEXPORT void autoprewarm_database_main(Datum main_arg);
 
@@ -419,6 +442,55 @@ apw_load_buffers(void)
 						apw_state->prewarmed_blocks, num_elements)));
 }
 
+/*
+ * Return the next block number of a specific relation and fork to read
+ * according to the array of BlockInfoRecord.
+ */
+static BlockNumber
+apw_read_stream_next_block(ReadStream *stream,
+						   void *callback_private_data,
+						   void *per_buffer_data)
+{
+	AutoPrewarmReadStreamData *p = callback_private_data;
+
+	while (p->pos < apw_state->prewarm_stop_idx)
+	{
+		BlockInfoRecord blk = p->block_info[p->pos];
+
+		CHECK_FOR_INTERRUPTS();
+
+		if (!have_free_buffer())
+			p->pos = apw_state->prewarm_stop_idx;
+
+		if (p->pos >= apw_state->prewarm_stop_idx)
+			return InvalidBlockNumber;
+
+		if (blk.database != p->database)
+			return InvalidBlockNumber;
+
+		if (blk.filenumber != p->filenumber)
+			return InvalidBlockNumber;
+
+		if (blk.forknum != p->forknum)
+			return InvalidBlockNumber;
+
+		p->pos++;
+
+		/*
+		 * Check whether blocknum is valid and within fork file size.
+		 * Fast-forward through any invalid blocks. We want `p->pos` to
+		 * reflect the location of the next relation or fork before ending the
+		 * stream.
+		 */
+		if (blk.blocknum >= p->nblocks)
+			continue;
+
+		return blk.blocknum;
+	}
+
+	return InvalidBlockNumber;
+}
+
 /*
  * Prewarm all blocks for one database or global objects (while connected to a
  * valid database).
@@ -467,8 +539,6 @@ autoprewarm_database_main(Datum main_arg)
 		Oid			reloid;
 		Relation	rel;
 
-		CHECK_FOR_INTERRUPTS();
-
 		StartTransactionCommand();
 
 		reloid = RelidByRelfilenumber(blk.tablespace, blk.filenumber);
@@ -509,6 +579,8 @@ autoprewarm_database_main(Datum main_arg)
 		{
 			ForkNumber	forknum = blk.forknum;
 			BlockNumber nblocks;
+			struct AutoPrewarmReadStreamData p;
+			ReadStream *stream;
 			Buffer		buf;
 
 			/*
@@ -539,32 +611,41 @@ autoprewarm_database_main(Datum main_arg)
 
 			nblocks = RelationGetNumberOfBlocksInFork(rel, blk.forknum);
 
-			/* Prewarm buffers. */
-			while (i < apw_state->prewarm_stop_idx &&
-				   blk.database == database &&
-				   blk.filenumber == filenumber &&
-				   blk.forknum == forknum &&
-				   have_free_buffer())
+			p = (struct AutoPrewarmReadStreamData)
 			{
-				CHECK_FOR_INTERRUPTS();
-
-				/* Check whether blocknum is valid and within fork file size. */
-				if (blk.blocknum >= nblocks)
-				{
-					blk = block_info[++i];
-					continue;
-				}
-
-				buf = ReadBufferExtended(rel, blk.forknum, blk.blocknum, RBM_NORMAL,
-										 NULL);
-
-				blk = block_info[++i];
-				if (!BufferIsValid(buf))
-					break;
+				.block_info = block_info,
+					.pos = i,
+					.database = database,
+					.filenumber = filenumber,
+					.forknum = forknum,
+					.nblocks = nblocks,
+			};
+
+			stream = read_stream_begin_relation(READ_STREAM_FULL,
+												NULL,
+												rel,
+												p.forknum,
+												apw_read_stream_next_block,
+												&p,
+												0);
 
+			/*
+			 * Loop until we've prewarmed all the blocks from this fork. The
+			 * read stream callback will check that we still have free buffers
+			 * before requesting each block from the read stream API.
+			 */
+			while ((buf = read_stream_next_buffer(stream, NULL)) != InvalidBuffer)
+			{
 				apw_state->prewarmed_blocks++;
 				ReleaseBuffer(buf);
 			}
+
+			Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+			read_stream_end(stream);
+
+			/* Advance i past all the blocks just prewarmed. */
+			i = p.pos;
+			blk = block_info[i];
 		}
 
 		relation_close(rel, AccessShareLock);
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 8f28d8ff28e..5ac290fae78 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -175,6 +175,7 @@ AttributeOpts
 AuthRequest
 AuthToken
 AutoPrewarmSharedState
+AutoPrewarmReadStreamData
 AutoVacOpts
 AutoVacuumShmemStruct
 AutoVacuumWorkItem
-- 
2.34.1

