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>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Andrey M. Borodin <x4mmm@yandex-team.ru> (earlier versions)
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>  (earlier versions)
Reviewed-by: Matheus Alcantara <mths.dev@pm.me> (earlier versions)
Discussion: https://postgr.es/m/flat/CAN55FZ3n8Gd%2BhajbL%3D5UkGzu_aHGRqnn%2BxktXq2fuds%3D1AOR6Q%40mail.gmail.com

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			tablespace;
+	RelFileNumber filenumber;
+	ForkNumber	forknum;
+	BlockNumber nblocks;
+} AutoPrewarmReadStreamData;
+
+
 PGDLLEXPORT void autoprewarm_main(Datum main_arg);
 PGDLLEXPORT void autoprewarm_database_main(Datum main_arg);
 
@@ -422,6 +445,54 @@ 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;
+
+	CHECK_FOR_INTERRUPTS();
+
+	while (p->pos < apw_state->prewarm_stop_idx)
+	{
+		BlockInfoRecord blk = p->block_info[p->pos];
+
+		if (!have_free_buffer())
+		{
+			p->pos = apw_state->prewarm_stop_idx;
+			return InvalidBlockNumber;
+		}
+
+		if (blk.tablespace != p->tablespace)
+			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 (and possibly also global objects, if
  * those got grouped with this database).
@@ -462,8 +533,6 @@ autoprewarm_database_main(Datum main_arg)
 		Oid			reloid;
 		Relation	rel;
 
-		CHECK_FOR_INTERRUPTS();
-
 		/*
 		 * All blocks between prewarm_start_idx and prewarm_stop_idx should
 		 * belong either to global objects or the same database.
@@ -510,6 +579,8 @@ autoprewarm_database_main(Datum main_arg)
 		{
 			ForkNumber	forknum = blk.forknum;
 			BlockNumber nblocks;
+			struct AutoPrewarmReadStreamData p;
+			ReadStream *stream;
 			Buffer		buf;
 
 			/*
@@ -540,32 +611,41 @@ autoprewarm_database_main(Datum main_arg)
 
 			nblocks = RelationGetNumberOfBlocksInFork(rel, blk.forknum);
 
-			/* Prewarm buffers. */
-			while (i < apw_state->prewarm_stop_idx &&
-				   blk.tablespace == tablespace &&
-				   blk.filenumber == filenumber &&
-				   blk.forknum == forknum &&
-				   have_free_buffer())
+			p = (struct AutoPrewarmReadStreamData)
 			{
-				CHECK_FOR_INTERRUPTS();
+				.block_info = block_info,
+					.pos = i,
+					.tablespace = tablespace,
+					.filenumber = filenumber,
+					.forknum = forknum,
+					.nblocks = nblocks,
+			};
 
-				/* 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;
+			stream = read_stream_begin_relation(READ_STREAM_DEFAULT |
+												READ_STREAM_USE_BATCHING,
+												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);
 			}
+
+			read_stream_end(stream);
+
+			/* Advance i past all the blocks just prewarmed. */
+			i = p.pos;
+			blk = block_info[i];
 		}
 
 		relation_close(rel, AccessShareLock);

src/tools/pgindent/typedefs.list

@@ -175,6 +175,7 @@ AttributeOpts
 AuthRequest
 AuthToken
 AutoPrewarmSharedState
+AutoPrewarmReadStreamData
 AutoVacOpts
 AutoVacuumShmemStruct
 AutoVacuumWorkItem