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Commit63e59c2

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In WAL replay, restore GIN metapage unconditionally to avoid torn page.
We don't take a full-page image of the GIN metapage; instead, the WAL recordcontains all the information required to reconstruct it from scratch. Butto avoid torn page hazards, we must re-initialize it from the WAL recordevery time, even if it already has a greater LSN, similar to how normal fullpage images are restored.This was highly unlikely to cause any problems in practice, because the GINmetapage is small. We rely on an update smaller than a 512 byte disk sectorto be atomic elsewhere, at least in pg_control. But better safe than sorry,and this would be easy to overlook if more fields are added to the metapageso that it's no longer small.Reported by Noah Misch. Backpatch to all supported versions.
1 parent080ad91 commit63e59c2

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‎src/backend/access/gin/ginxlog.c

Lines changed: 13 additions & 14 deletions
Original file line numberDiff line numberDiff line change
@@ -514,18 +514,20 @@ ginRedoUpdateMetapage(XLogRecPtr lsn, XLogRecord *record)
514514
Pagemetapage;
515515
Bufferbuffer;
516516

517+
/*
518+
* Restore the metapage. This is essentially the same as a full-page image,
519+
* so restore the metapage unconditionally without looking at the LSN, to
520+
* avoid torn page hazards.
521+
*/
517522
metabuffer=XLogReadBuffer(data->node,GIN_METAPAGE_BLKNO, false);
518523
if (!BufferIsValid(metabuffer))
519524
return;/* assume index was deleted, nothing to do */
520525
metapage=BufferGetPage(metabuffer);
521526

522-
if (!XLByteLE(lsn,PageGetLSN(metapage)))
523-
{
524-
memcpy(GinPageGetMeta(metapage),&data->metadata,sizeof(GinMetaPageData));
525-
PageSetLSN(metapage,lsn);
526-
PageSetTLI(metapage,ThisTimeLineID);
527-
MarkBufferDirty(metabuffer);
528-
}
527+
memcpy(GinPageGetMeta(metapage),&data->metadata,sizeof(GinMetaPageData));
528+
PageSetLSN(metapage,lsn);
529+
PageSetTLI(metapage,ThisTimeLineID);
530+
MarkBufferDirty(metabuffer);
529531

530532
if (data->ntuples>0)
531533
{
@@ -678,13 +680,10 @@ ginRedoDeleteListPages(XLogRecPtr lsn, XLogRecord *record)
678680
return;/* assume index was deleted, nothing to do */
679681
metapage=BufferGetPage(metabuffer);
680682

681-
if (!XLByteLE(lsn,PageGetLSN(metapage)))
682-
{
683-
memcpy(GinPageGetMeta(metapage),&data->metadata,sizeof(GinMetaPageData));
684-
PageSetLSN(metapage,lsn);
685-
PageSetTLI(metapage,ThisTimeLineID);
686-
MarkBufferDirty(metabuffer);
687-
}
683+
memcpy(GinPageGetMeta(metapage),&data->metadata,sizeof(GinMetaPageData));
684+
PageSetLSN(metapage,lsn);
685+
PageSetTLI(metapage,ThisTimeLineID);
686+
MarkBufferDirty(metabuffer);
688687

689688
/*
690689
* In normal operation, shiftList() takes exclusive lock on all the

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