postgres.git / summary / log / commit / refs

commit    86874a6dfc8b1878bede18437b1709fbe485a911
Author:   Tom Lane <tgl@sss.pgh.pa.us>
Date:     Mon Apr 17 18:22:06 2023 +0000
First released in: 16.0, 11.20, 12.15, 13.11, 14.8, 15.3

    Avoid trying to write an empty WAL record in log_newpage_range().
    
    If the last few pages in the specified range are empty (all zero),
    then log_newpage_range() could try to emit an empty WAL record
    containing no FPIs.  This at least upsets an Assert in
    ReserveXLogInsertLocation, and might perhaps have bad real-world
    consequences in non-assert builds.
    
    This has been broken since log_newpage_range() was introduced,
    but the case was hard if not impossible to hit before commit 3d6a98457
    decided it was okay to leave VM and FSM pages intentionally zero.
    Nonetheless, it seems prudent to back-patch.  log_newpage_range()
    was added in v12 but later back-patched, so this affects all
    supported branches.
    
    Matthias van de Meent, per report from Justin Pryzby
    
    Discussion: https://postgr.es/m/ZD1daibg4RF50IOj@telsasoft.com


 src/backend/access/transam/xloginsert.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
index b21679f09eb..cd85d4bcc72 100644
--- a/src/backend/access/transam/xloginsert.c
+++ b/src/backend/access/transam/xloginsert.c
@@ -1093,6 +1093,10 @@ log_newpage_range(Relation rel, ForkNumber forkNum,
 			blkno++;
 		}
 
+		/* Nothing more to do if all remaining blocks were empty. */
+		if (nbufs == 0)
+			break;
+
 		/* Write WAL record for this batch. */
 		XLogBeginInsert();
 


[parent: 7428aecddf18]