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Commitc6ade7a

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Prevent deadlock in ginRedoDeletePage()
On standby ginRedoDeletePage() can work concurrently with read-only queries.Those queries can traverse posting tree in two ways.1) Using rightlinks by ginStepRight(), which locks the next page before unlocking its left sibling.2) Using downlinks by ginFindLeafPage(), which locks at most one page at time.Original lock order was: page, parent, left sibling. That lock order candeadlock with ginStepRight(). In order to prevent deadlock this commit changeslock order to: left sibling, page, parent. Note, that position of parent inlocking order seems insignificant, because we only lock one page at time whiletraversing downlinks.Reported-by: Chen HuajunDiagnosed-by: Chen Huajun, Peter Geoghegan, Andrey BorodinDiscussion:https://postgr.es/m/31a702a.14dd.166c1366ac1.Coremail.chjischj%40163.comAuthor: Alexander KorotkovBackpatch-through: 9.4
1 parentfd83c83 commitc6ade7a

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‎src/backend/access/gin/ginxlog.c

Lines changed: 13 additions & 9 deletions
Original file line numberDiff line numberDiff line change
@@ -513,6 +513,19 @@ ginRedoDeletePage(XLogReaderState *record)
513513
Bufferlbuffer;
514514
Pagepage;
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516+
/*
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* Lock left page first in order to prevent possible deadlock with
518+
* ginStepRight().
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*/
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if (XLogReadBufferForRedo(record,2,&lbuffer)==BLK_NEEDS_REDO)
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{
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page=BufferGetPage(lbuffer);
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Assert(GinPageIsData(page));
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GinPageGetOpaque(page)->rightlink=data->rightLink;
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PageSetLSN(page,lsn);
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MarkBufferDirty(lbuffer);
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}
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if (XLogReadBufferForRedo(record,0,&dbuffer)==BLK_NEEDS_REDO)
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{
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page=BufferGetPage(dbuffer);
@@ -532,15 +545,6 @@ ginRedoDeletePage(XLogReaderState *record)
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MarkBufferDirty(pbuffer);
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}
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535-
if (XLogReadBufferForRedo(record,2,&lbuffer)==BLK_NEEDS_REDO)
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{
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page=BufferGetPage(lbuffer);
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Assert(GinPageIsData(page));
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GinPageGetOpaque(page)->rightlink=data->rightLink;
540-
PageSetLSN(page,lsn);
541-
MarkBufferDirty(lbuffer);
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}
543-
544548
if (BufferIsValid(lbuffer))
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UnlockReleaseBuffer(lbuffer);
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if (BufferIsValid(pbuffer))

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