Re: Hot standby, recovery infra

On Thu, 2009-01-29 at 09:34 +0200, Heikki Linnakangas wrote:

> It does *during recovery*, before InitXLogAccess is called. Yeah, it's
> harmless currently. It would be pretty hard to keep it up-to-date in
> bgwriter and other processes. I think it's better to keep it at 0,
> which is clearly an invalid value, than try to keep it up-to-date and
> risk using an old value. TimeLineID is not used in a lot of places,
> currently. It might be a good idea to add some "Assert(TimeLineID !=
> 0)" to places where it used.

Agreed. TimeLineID is a normal-running concept used for writing WAL.
Perhaps we should even solidify the meaning of TimeLineID == 0 as
"cannot write WAL".

I see a problem there for any process that exists both before and after
recovery ends, which includes bgwriter. In that case we must not flush
WAL before recovery ends, yet afterwards we *must* flush WAL. To do that
we *must* have a valid TimeLineID set.

I would suggest we put InitXLogAccess into IsRecoveryProcessingMode(),
so if the mode changes we immediately set everything we need to allow
XLogFlush() calls to work correctly.

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Simon Riggs www.2ndQuadrant.com
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