On Wed, Jun 15, 2016 at 12:44 AM, Robert Haas <robertmh...@gmail.com> wrote: > On Tue, Jun 14, 2016 at 8:11 AM, Robert Haas <robertmh...@gmail.com> wrote: >>>> I noticed that the tuples that it reported were always offset 1 in a >>>> page, and that the page always had a maxoff over a couple of hundred, >>>> and that we called record_corrupt_item because VM_ALL_VISIBLE returned >>>> true but HeapTupleSatisfiesVacuum on the first tuple returned >>>> HEAPTUPLE_DELETE_IN_PROGRESS instead of the expected HEAPTUPLE_LIVE. >>>> It did that because HEAP_XMAX_COMMITTED was not set and >>>> TransactionIdIsInProgress returned true for xmax. >>> >>> So this seems like it might be a visibility map bug rather than a bug >>> in the test code, but I'm not completely sure of that. How was it >>> legitimate to mark the page as all-visible if a tuple on the page >>> still had a live xmax? If xmax is live and not just a locker then the >>> tuple is not visible to the transaction that wrote xmax, at least. >> >> Ah, wait a minute. I see how this could happen. Hang on, let me >> update the pg_visibility patch. > > The problem should be fixed in the attached revision of > pg_check_visible. I think what happened is: > > 1. pg_check_visible computed an OldestXmin. > 2. Some transaction committed. > 3. VACUUM computed a newer OldestXmin and marked a page all-visible with it. > 4. pg_check_visible then used its older OldestXmin to check the > visibility of tuples on that page, and saw delete-in-progress as a > result. > > I added a guard against a similar scenario involving xmin in the last > version of this patch, but forgot that we need to protect xmax in the > same way. With this version of the patch, I can no longer get any > TIDs to pop up out of pg_check_visible in my testing. (I haven't run > your test script for lack of the proper Python environment...)
I can still reproduce the problem with this new patch. What I see is that the OldestXmin, the new RecomputedOldestXmin and the tuple's xmax are all the same. -- Thomas Munro http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
