Re: WalSndWakeup() and synchronous_commit=off

Hi,

On Monday, May 28, 2012 07:11:53 PM Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > Does anybody have a better idea than to either call WalSndWakeup() at
> > essentially the wrong places or calling it inside a critical section?
> >
> > Tom, what danger do you see from calling it in a critical section?
>
> My concern was basically that it might throw an error. Looking at the
> current implementation of SetLatch, it seems that's not possible, but
> I wonder whether we want to lock ourselves into that assumption.
The assumption is already made at several other places I think.
XLogSetAsyncXactLSN does a SetLatch and is called from critical sections;
several signal handlers call it without any attention to the context.

Requiring it to be called outside would make its usage considerably less
convenient and I don't really see what could change that would require to
throw non-panic errors.

> Still, if the alternatives are worse, maybe that's the best answer.
> If we do that, though, let's add comments to WalSndWakeup and SetLatch
> mentioning that they mustn't throw error.
Patch attached.

Greetings,

Andres

PS: Sorry for dropping the CC list before...

--
Andres Freund http://www.2ndQuadrant.com/
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