From 2a8e1ac598c864ac2775f33da21a117c363c6c7f Mon Sep 17 00:00:00 2001 From: Heikki Linnakangas Date: Thu, 17 Apr 2014 17:47:50 +0300 Subject: [PATCH] Set the all-visible flag on heap page before writing WAL record, not after. If we set the all-visible flag after writing WAL record, and XLogInsert takes a full-page image of the page, the image would not include the flag. We will then proceed to set the VM bit, which would then be set without the corresponding all-visible flag on the heap page. Found by comparing page images on master and standby, after writing/replaying each WAL record. (There is still a discrepancy: the all-visible flag won't be set after replaying the HEAP_CLEAN record, even though it is set in the master. However, it will be set when replaying the HEAP2_VISIBLE record and setting the VM bit, so the all-visible flag and VM bit are always consistent on the standby, even though they are momentarily out-of-sync with master) Backpatch to 9.3 where this code was introduced. --- src/backend/commands/vacuumlazy.c | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) diff --git a/src/backend/commands/vacuumlazy.c b/src/backend/commands/vacuumlazy.c index d5db917d97f..3870df606b7 100644 --- a/src/backend/commands/vacuumlazy.c +++ b/src/backend/commands/vacuumlazy.c @@ -1213,6 +1213,13 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer, PageRepairFragmentation(page); + /* + * Now that we have removed the dead tuples from the page, once again + * check if the page has become all-visible. + */ + if (heap_page_is_all_visible(onerel, buffer, &visibility_cutoff_xid)) + PageSetAllVisible(page); + /* * Mark buffer dirty before we write WAL. */ @@ -1231,14 +1238,13 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer, } /* - * Now that we have removed the dead tuples from the page, once again - * check if the page has become all-visible. + * All the changes to the heap page have been done. If the all-visible + * flag is now set, also set the VM bit. */ - if (!visibilitymap_test(onerel, blkno, vmbuffer) && - heap_page_is_all_visible(onerel, buffer, &visibility_cutoff_xid)) + if (PageIsAllVisible(page) && + !visibilitymap_test(onerel, blkno, vmbuffer)) { Assert(BufferIsValid(*vmbuffer)); - PageSetAllVisible(page); visibilitymap_set(onerel, blkno, buffer, InvalidXLogRecPtr, *vmbuffer, visibility_cutoff_xid); }