Re: NOTIFY does not work as expected

On Tue, Jul 3, 2018 at 12:30 PM, Jeff Janes <jeff(dot)janes(at)gmail(dot)com> wrote:

> On Tue, Jul 3, 2018 at 1:28 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> Jeff Janes <jeff(dot)janes(at)gmail(dot)com> writes:
>> > On Mon, Jul 2, 2018 at 4:33 PM, Andrey <parihaaraka(at)gmail(dot)com> wrote:
>> >> [ delayed receipt of notifications ]
>>
>> > I don't think this is a bug. I don't see that the docs promise one
>> > behavior over the other, so it is really a dealer's choice. Also, I
>> can't
>> > reliably reproduce the reported 9.6.2 behavior on my own 9.6.2 server.
>>
>> FWIW, it looks like a bug to me. I don't have time to investigate
>> further right now, though. It's also not at all clear whether the
>> issue is in the server or libpq or psql ...
>>
>
> In my hands, it bisects down to this:
>
> commit 4f85fde8eb860f263384fffdca660e16e77c7f76
> Author: Andres Freund <andres(at)anarazel(dot)de>
> Date: Tue Feb 3 22:25:20 2015 +0100
>
> Introduce and use infrastructure for interrupt processing during
> client reads.
>
> But that was committed in 9.5.dev, not between 9.6.2 and 9.6.9.
>
> It is on the server side. This is testing with psql, and it doesn't seem
> to matter which version of it. Maybe there is something between 9.6.2 and
> 9.6.9 that shows up with another client or more.
>

Further diagnosis here is that in the "working" case the client receives a
single packet from the server containing both the pg_sleep response, and
async response, in that order, and the client processes both of them. In
the "broken" case, the client receives a single packet from the server
containing the pg_sleep response, and processes it, and then blocks on user
input. The async response is immediately available in the next packet if
the client would ask for it, but the client doesn't do so.

If I am diagnosing the right problem, this still doesn't seem like a bug to
me.

Andey, what is it that you saw in Wireshark?

Cheers,

Jeff