On Thu, Dec 09, 2010 at 09:48:25AM +0000, Simon Riggs wrote: > On Fri, 2010-12-03 at 21:43 +0200, Heikki Linnakangas wrote: > > On 29.11.2010 08:10, Noah Misch wrote: > > > I have a hot_standby system and use it to bear the load of various > > > reporting > > > queries that take 15-60 minutes each. In an effort to avoid long pauses > > > in > > > recovery, I set a vacuum_defer_cleanup_age constituting roughly three > > > hours of > > > the master's transactions. Even so, I kept seeing recovery pause for the > > > duration of a long-running query. In each case, the culprit record was an > > > XLOG_BTREE_DELETE arising from on-the-fly deletion of an index tuple. The > > > attached test script demonstrates the behavior (on HEAD); the index tuple > > > reclamation conflicts with a concurrent "SELECT pg_sleep(600)" on the > > > standby. > > > > > > Since this inserting transaction aborts, HeapTupleSatisfiesVacuum reports > > > HEAPTUPLE_DEAD independent of vacuum_defer_cleanup_age. We go ahead and > > > remove > > > the index tuples. On the standby, btree_xlog_delete_get_latestRemovedXid > > > does > > > not regard the inserting-transaction outcome, so btree_redo proceeds to > > > conflict > > > with snapshots having visibility over that transaction. Could we > > > correctly > > > improve this by teaching btree_xlog_delete_get_latestRemovedXid to ignore > > > tuples > > > of aborted transactions and tuples inserted and deleted within one > > > transaction? > > @Noah Easily the best bug reported submitted in a long time. Thanks. > > > Seems reasonable. HeapTupleHeaderAdvanceLatestRemovedXid() will need > > similar treatment. Actually, btree_xlog_delete_get_latestRemovedXid() > > could just call HeapTupleHeaderAdvanceLatestRemoveXid(). > > Yes, it applies to other cases also. Thanks for the suggestion. > > Fix committed. Please double-check my work, committed early since I'm > about to jump on a plane.
Thanks for making that change. For my understanding, why does the xmin == xmax special case in HeapTupleHeaderAdvanceLatestRemoveXid not require !HEAP_UPDATED, as the corresponding case in HeapTupleSatisfiesVacuum requires? I can neither think of a recipe for triggering a problem as the code stands, nor come up with a sound explanation for why no such recipe can exist. nm
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