Re: BUG #4879: bgwriter fails to fsync the file in recovery mode

On Thu, 2009-06-25 at 13:25 -0400, Tom Lane wrote:
> Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
> > It's tempting to just remove the "!isRedo" condition, but then we have
> > another problem: if bgwriter hasn't been started yet, and the shmem
> > queue is full, we get stuck in register_unlink() trying to send the
> > message and failing.
>
> > In archive recovery, we always start bgwriter at the beginning of WAL
> > replay. In crash recovery, we don't start bgwriter until the end of wAL
> > replay. So we could change the "!isRedo" condition to
> > "!InArchiveRecovery". It's not a very clean solution, but it's simple.
>
> I looked through the callers of smgrdounlink(), and found that
> FinishPreparedTransaction passes isRedo = true. I'm not sure at the
> moment what the reasoning behind that was, but it does seem to mean that
> checking InArchiveRecovery instead of isRedo may not be quite right.

I think that's because FinishPreparedTransaction() implicitly assumes
that if a file still exists we are in recovery. I can't comment on
whether that is necessarily true for some reason, but it doesn't sound
like it is a safe assumption. I would guess it's using isRedo as an
implicit override rather than using the correct meaning of the variable.

--
Simon Riggs www.2ndQuadrant.com
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