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Commit95aa823

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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 XLogInserttakes 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 thecorresponding all-visible flag on the heap page.Found by comparing page images on master and standby, after writing/replayingeach WAL record. (There is still a discrepancy: the all-visible flag won'tbe set after replaying the HEAP_CLEAN record, even though it is set in themaster. However, it will be set when replaying the HEAP2_VISIBLE record andsetting the VM bit, so the all-visible flag and VM bit are always consistenton the standby, even though they are momentarily out-of-sync with master)Backpatch to 9.3 where this code was introduced.
1 parentaa0a519 commit95aa823

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‎src/backend/commands/vacuumlazy.c‎

Lines changed: 11 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -1206,6 +1206,13 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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PageRepairFragmentation(page);
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1209+
/*
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* Now that we have removed the dead tuples from the page, once again
1211+
* check if the page has become all-visible.
1212+
*/
1213+
if (heap_page_is_all_visible(buffer,&visibility_cutoff_xid))
1214+
PageSetAllVisible(page);
1215+
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/*
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* Mark buffer dirty before we write WAL.
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*/
@@ -1224,14 +1231,13 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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}
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/*
1227-
*Now that we have removedthedead tuples from the page, once again
1228-
*check if the page has become all-visible.
1234+
*All the changes totheheap page have been done. If the all-visible
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*flag is now set, also set the VM bit.
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*/
1230-
if (!visibilitymap_test(onerel,blkno,vmbuffer)&&
1231-
heap_page_is_all_visible(buffer,&visibility_cutoff_xid))
1237+
if (PageIsAllVisible(page)&&
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!visibilitymap_test(onerel,blkno,vmbuffer))
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{
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Assert(BufferIsValid(*vmbuffer));
1234-
PageSetAllVisible(page);
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visibilitymap_set(onerel,blkno,buffer,InvalidXLogRecPtr,*vmbuffer,
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visibility_cutoff_xid);
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}

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