Re: xlog.c: WALInsertLock vs. WALWriteLock

On Tue, Oct 26, 2010 at 3:00 PM, Josh Berkus <josh@agliodbs.com> wrote:
>
>> I agree that the standby might get ahead, but this doesn't necessarily
>> lead to database corruption. Here, the interesting case is what happens
>> when the primary fails, which can lead to *either* of the following two
>> cases:
>> 1) The standby, due to some triggering mechanism, becomes the new
>> primary. In this case, even if the standby was ahead, its fine.
>> 2) The primary comes back as primary. In this case, the standby will
>> connect again to the primary. At this point, *if* somehow we are able to
>> detect that the standby is ahead, then we should abort the standby and
>> create a standby from scratch.
>
> Yes.  And we weren't able to implement that for 9.0.  It's worth
> revisiting for 9.1.  In fact, the issue of "is the standby ahead of the
> master" has come up repeatedly in potential failure scenarios; I think
> we're going to need a fairly bulletproof method to determine this.

Agreed.

--
Robert Haas
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