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 this rule is wrong. I think the rule ought to be something like "if the XMAX_INVALID bit is set, then reset whatever is there if there is something; if the bit is not set, proceed as today". Otherwise we risk reading garbage, which is what is happening in this case. -- Álvaro Herrera http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
