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Commit47ad791
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Fix bugs in Serializable Snapshot Isolation.
Change the way UPDATEs are handled. Instead of maintaining a chain oftuple-level locks in shared memory, copy any existing locks on the oldtuple to the new tuple at UPDATE. Any existing page-level lock needs tobe duplicated too, as a lock on the new tuple. That was neglectedpreviously.Store xmin on tuple-level predicate locks, to distinguish a lock on an oldalready-recycled tuple from a new tuple at the same physical location.Failure to distinguish them caused loops in the tuple-lock chains, asreported by YAMAMOTO Takashi. Although we don't use the chain representationof UPDATEs anymore, it seems like a good idea to store the xmin to avoidsome false positives if no other reason.CheckSingleTargetForConflictsIn now correctly handles the case where a lockthat's being held is not reflected in the local lock table. That happensif another backend acquires a lock on our behalf due to an UPDATE or a pagesplit.PredicateLockPageCombine now retains locks for the page that is beingremoved, rather than removing them. This prevents a potentially dangerousfalse-positive inconsistency where the local lock table believes that a lockis held, but it is actually not.Dan Ports and Kevin Grittner1 parent16143d6 commit47ad791
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