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Commitecac0e2

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Do all-visible handling in lazy_vacuum_page() outside its critical section.
Sincefdf9e21 lazy_vacuum_page() rechecks the all-visible statusof pages in the second pass over the heap. It does so inside acritical section, but both visibilitymap_test() andheap_page_is_all_visible() perform operations that should not happeninside one. The former potentially performs IO and both potentially domemory allocations.To fix, simply move all the all-visible handling outside the criticalsection. Doing so means that the PD_ALL_VISIBLE on the page won't beincluded in the full page image of the HEAP2_CLEAN record anymore. Butthat's fine, the flag will be set by the HEAP2_VISIBLE logged later.Backpatch to 9.3 where the problem was introduced. The bug only cameto light due to the assertion added in4a170ee and isn't likely tocause problems in production scenarios. The worst outcome is aavoidable PANIC restart.This also gets rid of the difference in the order of operationsbetween master and standby mentioned in2a8e1ac.Per reports from David Leverton and Keith Fiske in bug #10533.
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‎src/backend/commands/vacuumlazy.c

Lines changed: 17 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -1213,13 +1213,6 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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12141214
PageRepairFragmentation(page);
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1216-
/*
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* Now that we have removed the dead tuples from the page, once again
1218-
* check if the page has become all-visible.
1219-
*/
1220-
if (heap_page_is_all_visible(onerel,buffer,&visibility_cutoff_xid))
1221-
PageSetAllVisible(page);
1222-
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/*
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* Mark buffer dirty before we write WAL.
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*/
@@ -1237,6 +1230,23 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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PageSetLSN(page,recptr);
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}
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1233+
/*
1234+
* End critical section, so we safely can do visibility tests (which
1235+
* possibly need to perform IO and allocate memory!). If we crash now the
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* page (including the corresponding vm bit) might not be marked all
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* visible, but that's fine. A later vacuum will fix that.
1238+
*/
1239+
END_CRIT_SECTION();
1240+
1241+
/*
1242+
* Now that we have removed the dead tuples from the page, once again
1243+
* check if the page has become all-visible. The page is already marked
1244+
* dirty, exclusively locked, and, if needed, a full page image has been
1245+
* emitted in the log_heap_clean() above.
1246+
*/
1247+
if (heap_page_is_all_visible(onerel,buffer,&visibility_cutoff_xid))
1248+
PageSetAllVisible(page);
1249+
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/*
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* All the changes to the heap page have been done. If the all-visible
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* flag is now set, also set the VM bit.
@@ -1249,8 +1259,6 @@ lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
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visibility_cutoff_xid);
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}
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1252-
END_CRIT_SECTION();
1253-
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returntupindex;
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}
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