From: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
---|---|
To: | Andres Freund <andres(at)2ndquadrant(dot)com> |
Cc: | Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: MultiXactId error after upgrade to 9.3.4 |
Date: | 2014-04-23 18:01:02 |
Message-ID: | 20140423180102.GP25695@eldon.alvh.no-ip.org |
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Lists: | pgsql-hackers |
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
Attachment | Content-Type | Size |
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no-freeze-invalid-multi.patch | text/x-diff | 607 bytes |
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