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Commit2fa8ba3

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Fix handling of all-zero pages in SP-GiST vacuum.
SP-GiST initialized an all-zeros page at vacuum, but that was notWAL-logged, which is not safe. You might get a torn page write, when it getsflushed to disk, and end-up with a half-initialized index page. To fix,leave it in the all-zeros state, and add it to the FSM. It will beinitialized when reused. Also don't set the page-deleted flag when recyclingan empty page. That was also not WAL-logged, and a torn write of that wouldcause the page to have an invalid checksum.Backpatch to 9.2, where SP-GiST indexes were added.
1 parent6a0a388 commit2fa8ba3

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2 files changed

+10
-21
lines changed

2 files changed

+10
-21
lines changed

‎src/backend/access/spgist/spgvacuum.c

Lines changed: 8 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -621,14 +621,10 @@ spgvacuumpage(spgBulkDeleteState *bds, BlockNumber blkno)
621621
{
622622
/*
623623
* We found an all-zero page, which could happen if the database
624-
* crashed just after extending the file.Initialize and recycle it.
624+
* crashed just after extending the file.Recycle it.
625625
*/
626-
SpGistInitBuffer(buffer,0);
627-
SpGistPageSetDeleted(page);
628-
/* We don't bother to WAL-log this action; easy to redo */
629-
MarkBufferDirty(buffer);
630626
}
631-
elseif (SpGistPageIsDeleted(page))
627+
elseif (PageIsEmpty(page))
632628
{
633629
/* nothing to do */
634630
}
@@ -654,30 +650,23 @@ spgvacuumpage(spgBulkDeleteState *bds, BlockNumber blkno)
654650
/*
655651
* The root pages must never be deleted, nor marked as available in FSM,
656652
* because we don't want them ever returned by a search for a place to put
657-
* a new tuple. Otherwise, check for empty/deletable page, and make sure
658-
*FSMknows about it.
653+
* a new tuple. Otherwise, check for empty page, and make sure the FSM
654+
* knows about it.
659655
*/
660656
if (!SpGistBlockIsRoot(blkno))
661657
{
662-
/* If page is now empty, mark it deleted */
663-
if (PageIsEmpty(page)&& !SpGistPageIsDeleted(page))
664-
{
665-
SpGistPageSetDeleted(page);
666-
/* We don't bother to WAL-log this action; easy to redo */
667-
MarkBufferDirty(buffer);
668-
}
669-
670-
if (SpGistPageIsDeleted(page))
658+
if (PageIsEmpty(page))
671659
{
672660
RecordFreeIndexPage(index,blkno);
673661
bds->stats->pages_deleted++;
674662
}
675663
else
664+
{
665+
SpGistSetLastUsedPage(index,buffer);
676666
bds->lastFilledBlock=blkno;
667+
}
677668
}
678669

679-
SpGistSetLastUsedPage(index,buffer);
680-
681670
UnlockReleaseBuffer(buffer);
682671
}
683672

‎src/include/access/spgist_private.h

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -48,14 +48,14 @@ typedef SpGistPageOpaqueData *SpGistPageOpaque;
4848

4949
/* Flag bits in page special space */
5050
#defineSPGIST_META(1<<0)
51-
#defineSPGIST_DELETED(1<<1)
51+
#defineSPGIST_DELETED(1<<1)/* never set, but keep for backwards
52+
* compatibility */
5253
#defineSPGIST_LEAF(1<<2)
5354
#defineSPGIST_NULLS(1<<3)
5455

5556
#defineSpGistPageGetOpaque(page) ((SpGistPageOpaque) PageGetSpecialPointer(page))
5657
#defineSpGistPageIsMeta(page) (SpGistPageGetOpaque(page)->flags & SPGIST_META)
5758
#defineSpGistPageIsDeleted(page) (SpGistPageGetOpaque(page)->flags & SPGIST_DELETED)
58-
#defineSpGistPageSetDeleted(page) (SpGistPageGetOpaque(page)->flags |= SPGIST_DELETED)
5959
#defineSpGistPageIsLeaf(page) (SpGistPageGetOpaque(page)->flags & SPGIST_LEAF)
6060
#defineSpGistPageStoresNulls(page) (SpGistPageGetOpaque(page)->flags & SPGIST_NULLS)
6161

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