Re: Immediate standby promotion

On 14 August 2014 20:27, Robert Haas  wrote:
> On Thu, Aug 14, 2014 at 10:12 AM, Tom Lane  wrote:
>> Fujii Masao  writes:
>>> I'd like to propose to add new option "--immediate" to pg_ctl promote.
>>> When this option is set, recovery ignores any WAL data which have not
>>> been replayed yet and exits immediately. Patch attached.
>>
>>> This promotion is faster than normal one but can cause data loss.
>>
>> TBH, I cannot imagine a situation where that would be a sane thing to do.
>> If you have WAL, why would you not replay what you have?  The purpose
>> of a database is to preserve your data, not randomly throw it away.
>
> I've wanted this a number of times, so I think it's quite sane.

"fast" promotion was actually a supported option in r8 of Postgres but
this option was removed when we implemented streaming replication in
r9.0

The *rough* requirement is sane, but that's not the same thing as
saying this exact patch makes sense.

If you are paused and you can see that WAL up ahead is damaged, then
YES, you do want to avoid applying it. That is possible by setting a
PITR target so that recovery stops at a precise location specified by
you. As an existing option is it better than the blunt force trauma
suggested here.

If you really don't care, just shutdown server, resetxlog and start
her up - again, no need for new option.

Anyway, my view is that this is a blunt instrument to do something we
can already do.

-- Simon Riggs                   http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training & Services