Re: Race conditions in 019_replslot_limit.pl

Andres Freund <andres@anarazel.de> writes:
> On 2022-02-18 18:15:21 -0500, Tom Lane wrote:
>> Perhaps it'd be sensible to do this only in debugging (ie Assert)
>> builds?

> That seems not great, because it pretty clearly can lead to hangs, which is
> problematic in tests too. What about using pq_flush_if_writable()? In nearly
> all situations that'd still push the failure to the client.

That'd be okay by me.

> We'd also need to add pq_endmessage_noblock(), because the pq_endmessage()
> obviously tries to send (as in the backtrace upthread) if the output buffer is
> large enough, which it often will be in walsender.

I don't see that as "obvious".  If we're there, we do not have an
error situation.

> I guess we could try to flush in a blocking manner sometime later in the
> shutdown sequence, after we've released resources? But I'm doubtful it's a
> good idea, we don't really want to block waiting to exit when e.g. the network
> connection is dead without the TCP stack knowing.

I think you are trying to move in the direction of possibly exiting
without ever sending at all, which does NOT seem like an improvement.

            regards, tom lane