Use streaming read I/O in heap amcheck

Instead of directly invoking ReadBuffer() for each unskippable block in
the heap relation, verify_heapam() now uses the read stream API to
acquire the next buffer to check for corruption.

Author: Matheus Alcantara <matheusssilv97@gmail.com>
Co-authored-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Reviewed-by: jian he <jian.universality@gmail.com>
Discussion: https://postgr.es/m/flat/CAFY6G8eLyz7%2BsccegZYFj%3D5tAUR-GZ9uEq4Ch5gvwKqUwb_hCA%40mail.gmail.com

contrib/amcheck/verify_heapam.c

@@ -25,6 +25,7 @@
 #include "miscadmin.h"
 #include "storage/bufmgr.h"
 #include "storage/procarray.h"
+#include "storage/read_stream.h"
 #include "utils/builtins.h"
 #include "utils/fmgroids.h"
 #include "utils/rel.h"
@@ -118,7 +119,10 @@ typedef struct HeapCheckContext
 	Relation	valid_toast_index;
 	int			num_toast_indexes;
 
-	/* Values for iterating over pages in the relation */
+	/*
+	 * Values for iterating over pages in the relation. `blkno` is the most
+	 * recent block in the buffer yielded by the read stream API.
+	 */
 	BlockNumber blkno;
 	BufferAccessStrategy bstrategy;
 	Buffer		buffer;
@@ -153,7 +157,32 @@ typedef struct HeapCheckContext
 	Tuplestorestate *tupstore;
 } HeapCheckContext;
 
+/*
+ * The per-relation data provided to the read stream API for heap amcheck to
+ * use in its callback for the SKIP_PAGES_ALL_FROZEN and
+ * SKIP_PAGES_ALL_VISIBLE options.
+ */
+typedef struct HeapCheckReadStreamData
+{
+	/*
+	 * `range` is used by all SkipPages options. SKIP_PAGES_NONE uses the
+	 * default read stream callback, block_range_read_stream_cb(), which takes
+	 * a BlockRangeReadStreamPrivate as its callback_private_data. `range`
+	 * keeps track of the current block number across
+	 * read_stream_next_buffer() invocations.
+	 */
+	BlockRangeReadStreamPrivate range;
+	SkipPages	skip_option;
+	Relation	rel;
+	Buffer	   *vmbuffer;
+} HeapCheckReadStreamData;
+
+
 /* Internal implementation */
+static BlockNumber heapcheck_read_stream_next_unskippable(ReadStream *stream,
+														  void *callback_private_data,
+														  void *per_buffer_data);
+
 static void check_tuple(HeapCheckContext *ctx,
 						bool *xmin_commit_status_ok,
 						XidCommitStatus *xmin_commit_status);
@@ -231,6 +260,11 @@ verify_heapam(PG_FUNCTION_ARGS)
 	BlockNumber last_block;
 	BlockNumber nblocks;
 	const char *skip;
+	ReadStream *stream;
+	int			stream_flags;
+	ReadStreamBlockNumberCB stream_cb;
+	void	   *stream_data;
+	HeapCheckReadStreamData stream_skip_data;
 
 	/* Check supplied arguments */
 	if (PG_ARGISNULL(0))
@@ -404,7 +438,35 @@ verify_heapam(PG_FUNCTION_ARGS)
 	if (TransactionIdIsNormal(ctx.relfrozenxid))
 		ctx.oldest_xid = ctx.relfrozenxid;
 
-	for (ctx.blkno = first_block; ctx.blkno <= last_block; ctx.blkno++)
+	/* Now that `ctx` is set up, set up the read stream */
+	stream_skip_data.range.current_blocknum = first_block;
+	stream_skip_data.range.last_exclusive = last_block + 1;
+	stream_skip_data.skip_option = skip_option;
+	stream_skip_data.rel = ctx.rel;
+	stream_skip_data.vmbuffer = &vmbuffer;
+
+	if (skip_option == SKIP_PAGES_NONE)
+	{
+		stream_cb = block_range_read_stream_cb;
+		stream_flags = READ_STREAM_SEQUENTIAL | READ_STREAM_FULL;
+		stream_data = &stream_skip_data.range;
+	}
+	else
+	{
+		stream_cb = heapcheck_read_stream_next_unskippable;
+		stream_flags = READ_STREAM_DEFAULT;
+		stream_data = &stream_skip_data;
+	}
+
+	stream = read_stream_begin_relation(stream_flags,
+										ctx.bstrategy,
+										ctx.rel,
+										MAIN_FORKNUM,
+										stream_cb,
+										stream_data,
+										0);
+
+	while ((ctx.buffer = read_stream_next_buffer(stream, NULL)) != InvalidBuffer)
 	{
 		OffsetNumber maxoff;
 		OffsetNumber predecessor[MaxOffsetNumber];
@@ -417,30 +479,11 @@ verify_heapam(PG_FUNCTION_ARGS)
 
 		memset(predecessor, 0, sizeof(OffsetNumber) * MaxOffsetNumber);
 
-		/* Optionally skip over all-frozen or all-visible blocks */
+		/* Lock the next page. */
-		if (skip_option != SKIP_PAGES_NONE)
+		Assert(BufferIsValid(ctx.buffer));
-		{
-			int32		mapbits;
-
-			mapbits = (int32) visibilitymap_get_status(ctx.rel, ctx.blkno,
-													   &vmbuffer);
-			if (skip_option == SKIP_PAGES_ALL_FROZEN)
-			{
-				if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
-					continue;
-			}
-
-			if (skip_option == SKIP_PAGES_ALL_VISIBLE)
-			{
-				if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
-					continue;
-			}
-		}
-
-		/* Read and lock the next page. */
-		ctx.buffer = ReadBufferExtended(ctx.rel, MAIN_FORKNUM, ctx.blkno,
-										RBM_NORMAL, ctx.bstrategy);
 		LockBuffer(ctx.buffer, BUFFER_LOCK_SHARE);
+
+		ctx.blkno = BufferGetBlockNumber(ctx.buffer);
 		ctx.page = BufferGetPage(ctx.buffer);
 
 		/* Perform tuple checks */
@@ -799,6 +842,10 @@ verify_heapam(PG_FUNCTION_ARGS)
 			break;
 	}
 
+	/* Ensure that the stream is completely read */
+	Assert(read_stream_next_buffer(stream, NULL) == InvalidBuffer);
+	read_stream_end(stream);
+
 	if (vmbuffer != InvalidBuffer)
 		ReleaseBuffer(vmbuffer);
 
@@ -815,6 +862,42 @@ verify_heapam(PG_FUNCTION_ARGS)
 	PG_RETURN_NULL();
 }
 
+/*
+ * Heap amcheck's read stream callback for getting the next unskippable block.
+ * This callback is only used when 'all-visible' or 'all-frozen' is provided
+ * as the skip option to verify_heapam(). With the default 'none',
+ * block_range_read_stream_cb() is used instead.
+ */
+static BlockNumber
+heapcheck_read_stream_next_unskippable(ReadStream *stream,
+									   void *callback_private_data,
+									   void *per_buffer_data)
+{
+	HeapCheckReadStreamData *p = callback_private_data;
+
+	/* Loops over [current_blocknum, last_exclusive) blocks */
+	for (BlockNumber i; (i = p->range.current_blocknum++) < p->range.last_exclusive;)
+	{
+		uint8		mapbits = visibilitymap_get_status(p->rel, i, p->vmbuffer);
+
+		if (p->skip_option == SKIP_PAGES_ALL_FROZEN)
+		{
+			if ((mapbits & VISIBILITYMAP_ALL_FROZEN) != 0)
+				continue;
+		}
+
+		if (p->skip_option == SKIP_PAGES_ALL_VISIBLE)
+		{
+			if ((mapbits & VISIBILITYMAP_ALL_VISIBLE) != 0)
+				continue;
+		}
+
+		return i;
+	}
+
+	return InvalidBlockNumber;
+}
+
 /*
  * Shared internal implementation for report_corruption and
  * report_toast_corruption.

src/tools/pgindent/typedefs.list

@@ -1169,6 +1169,7 @@ HeadlineJsonState
 HeadlineParsedText
 HeadlineWordEntry
 HeapCheckContext
+HeapCheckReadStreamData
 HeapPageFreeze
 HeapScanDesc
 HeapTuple