On Tue, Jun 14, 2016 at 2:53 AM, Thomas Munro <thomas.mu...@enterprisedb.com> wrote: > On Tue, Jun 14, 2016 at 4:02 AM, Robert Haas <robertmh...@gmail.com> wrote: >> On Sat, Jun 11, 2016 at 5:00 PM, Robert Haas <robertmh...@gmail.com> wrote: >>>> How about changing the return tuple of heap_prepare_freeze_tuple to >>>> a bitmap? Two flags: "Freeze [not] done" and "[No] more freezing >>>> needed" >>> >>> Yes, I think something like that sounds about right. >> >> Here's a patch. I took the approach of adding a separate bool out >> parameter instead. I am also attaching an update of the >> check-visibility patch which responds to assorted review comments and >> adjusting it for the problems found on Friday which could otherwise >> lead to false positives. I'm still getting occasional TIDs from the >> pg_check_visible() function during pgbench runs, though, so evidently >> not all is well with the world. > > I'm still working out how half this stuff works, but I managed to get > pg_check_visible() to spit out a row every few seconds with the > following brute force approach: > > CREATE TABLE foo (n int); > INSERT INTO foo SELECT generate_series(1, 100000); > > Three client threads (see attached script): > 1. Run VACUUM in a tight loop. > 2. Run UPDATE foo SET n = n + 1 in a tight loop. > 3. Run SELECT pg_check_visible('foo'::regclass) in a tight loop, and > print out any rows it produces. > > 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. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers