Subject: [PATCH v7a 3/8] Fix off-by-one error in read IO tracing

From: Melanie Plageman <[email-masked]>
Date: Mon, 16 Mar 2026 16:50:56 -0400

AsyncReadBuffer()'s no-IO needed path passed
TRACE_POSTGRESQL_BUFFER_READ_DONE the wrong block number because it had
already incremented operation->nblocks_done. Fix by folding the
nblocks_done offset into the blocknum local variable at initialization.

Author: Melanie Plageman <[email-masked]>
Reviewed-by: Andres Freund <[email-masked]>
Discussion: https://postgr.es/m/u73un3xeljr4fiidzwi4ikcr6vm7oqugn4fo5vqpstjio6anl2%40hph6fvdiiria
---
 src/backend/storage/buffer/bufmgr.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 00bc609529a..10afae1990b 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -1875,10 +1875,10 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress)
 {
 	Buffer	   *buffers = &operation->buffers[0];
 	int			flags = operation->flags;
-	BlockNumber blocknum = operation->blocknum;
 	ForkNumber	forknum = operation->forknum;
 	char		persistence = operation->persistence;
 	int16		nblocks_done = operation->nblocks_done;
+	BlockNumber blocknum = operation->blocknum + nblocks_done;
 	Buffer	   *io_buffers = &operation->buffers[nblocks_done];
 	int			io_buffers_len = 0;
 	PgAioHandle *ioh;
@@ -1990,7 +1990,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress)
 		 * must have started out as a miss in PinBufferForBlock(). The other
 		 * backend will track this as a 'read'.
 		 */
-		TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, blocknum + operation->nblocks_done,
+		TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, blocknum,
 										  operation->smgr->smgr_rlocator.locator.spcOid,
 										  operation->smgr->smgr_rlocator.locator.dbOid,
 										  operation->smgr->smgr_rlocator.locator.relNumber,
@@ -2062,7 +2062,7 @@ AsyncReadBuffers(ReadBuffersOperation *operation, int *nblocks_progress)
 		 */
 		io_start = pgstat_prepare_io_time(track_io_timing);
 		smgrstartreadv(ioh, operation->smgr, forknum,
-					   blocknum + nblocks_done,
+					   blocknum,
 					   io_pages, io_buffers_len);
 		pgstat_count_io_op_time(io_object, io_context, IOOP_READ,
 								io_start, 1, io_buffers_len * BLCKSZ);
-- 
2.53.0.1.gb2826b52eb

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	filename="v7a-0004-Pass-io_object-and-io_context-through-to-PinBuff.patch"