Re: pg_sleep() doesn't work well with recovery conflict interrupts. - Mailing list pgsql-hackers

On 2014-05-30 10:30:42 +0530, Amit Kapila wrote:
> On Wed, May 28, 2014 at 8:53 PM, Andres Freund <andres@2ndquadrant.com>
> wrote:
> > Hi,
> >
> > Since a64ca63e59c11d8fe6db24eee3d82b61db7c2c83 pg_sleep() uses
> > WaitLatch() to wait. That's fine in itself. But
> > procsignal_sigusr1_handler, which is used e.g. when resolving recovery
> > conflicts, doesn't unconditionally do a SetLatch().
> > That means that we'll we'll currently not be able to cancel conflicting
> > backends during recovery for 10min. Now, I don't think that'll happen
> > too often in practice, but it's still annoying.
> 
> How will such a situation occur, aren't we using pg_usleep during
> RecoveryConflict functions
> (ex. in ResolveRecoveryConflictWithVirtualXIDs)?

I am not sure what you mean. pg_sleep() is the SQL callable function, a
different thing to pg_usleep(). The latter isn't interruptible on all
platforms, but the sleep times should be short enough for that not to
matter.
I am pretty sure by now that the sane fix for this is to add a
SetLatch() call to RecoveryConflictInterrupt(). All the signal handlers
that deal with query cancelation et al. do so, so it seems right that
RecoveryConflictInterrupt() does so as well.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
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