Andres Freund wrote: > On 2014-03-31 08:54:53 -0300, Alvaro Herrera wrote: > > My conclusion here is that some part of the code is failing to examine > > XMAX_INVALID before looking at the value stored in xmax itself. There > > ought to be a short-circuit. Fortunately, this bug should be pretty > > harmless. > > > > .. and after looking, I'm fairly sure the bug is in > > heap_tuple_needs_freeze. > > heap_tuple_needs_freeze() isn't *allowed* to look at > XMAX_INVALID. Otherwise it could miss freezing something still visible > on a standby or after an eventual crash.
I think what we should do here is that if we see that XMAX_INVALID is set, we just reset everything to zero without checking the multixact contents. Something like the attached (warning: hand-edited, line numbers might be bogus) I still don't know under what circumstances this situation could arise. This seems most strange to me. I would wonder about this to be just papering over a different bug elsewhere, except that we know this tuple comes from a pg_upgraded table and so I think the only real solution is to cope. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index 9283b70..72602fd 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -5585,7 +5602,12 @@ heap_prepare_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid, */ xid = HeapTupleHeaderGetRawXmax(tuple); - if (tuple->t_infomask & HEAP_XMAX_IS_MULTI) + if ((tuple->t_infomask & HEAP_XMAX_IS_MULTI) && + (tuple->t_infomask & HEAP_XMAX_INVALID)) + { + freeze_xmax = true; + } + else if (tuple->t_infomask & HEAP_XMAX_IS_MULTI) { TransactionId newxmax; uint16 flags;
-- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers