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Commit 47ad791

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hlinnakahlinnaka
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Fix bugs in Serializable Snapshot Isolation.
Change the way UPDATEs are handled. Instead of maintaining a chain of tuple-level locks in shared memory, copy any existing locks on the old tuple to the new tuple at UPDATE. Any existing page-level lock needs to be duplicated too, as a lock on the new tuple. That was neglected previously. Store xmin on tuple-level predicate locks, to distinguish a lock on an old already-recycled tuple from a new tuple at the same physical location. Failure to distinguish them caused loops in the tuple-lock chains, as reported by YAMAMOTO Takashi. Although we don't use the chain representation of UPDATEs anymore, it seems like a good idea to store the xmin to avoid some false positives if no other reason. CheckSingleTargetForConflictsIn now correctly handles the case where a lock that's being held is not reflected in the local lock table. That happens if another backend acquires a lock on our behalf due to an UPDATE or a page split. PredicateLockPageCombine now retains locks for the page that is being removed, rather than removing them. This prevents a potentially dangerous false-positive inconsistency where the local lock table believes that a lock is held, but it is actually not. Dan Ports and Kevin Grittner
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‎src/backend/access/nbtree/nbtree.c

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Original file line numberDiff line numberDiff line change
@@ -824,7 +824,6 @@ btvacuumpage(BTVacState *vstate, BlockNumber blkno, BlockNumber orig_blkno)
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if (_bt_page_recyclable(page))
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{
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/* Okay to recycle this page */
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Assert(!PageIsPredicateLocked(rel, blkno));
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RecordFreeIndexPage(rel, blkno);
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vstate->totFreePages++;
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stats->pages_deleted++;

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