Re: Fix 035_standby_logical_decoding.pl race conditions

Hi Kuroda-san,

On Mon, Mar 24, 2025 at 04:54:21AM +0000, Hayato Kuroda (Fujitsu) wrote:
> > So, I'm not sure I like the idea that much, but thinking out loud: I wonder if
> > we could bypass the "active" slot checks in 16 and 17 and use injection points as
> > proposed as of 18 (as we need the injection points changes proposed in 0001
> > up-thread). Thoughts?
>
> I do not have other idea neither. I checked your patch set could solve the issue.

Thanks for looking at it!

> Comments for the patch:
> I'm not sure whether new API is really needed. Isn't it enough to use both
> injection_points_wakeup() and injection_points_detach()?

I think that the proposed changes are needed as they fix 2 issues that I hit
while working on 0002:

1. ensure that no process can wait in between wakeup() and detach().

2. If the walsender is waiting on the injection point and the logical slot
is conflicting, then the walsender process is killed and so it is not able to
"empty" it's injection slot. So the next injection_wait() should reuse this slot
(instead of using an empty one).

> Also, another check whether the extension can be installed for the node is required.
> Please see 041_checkpoint_at_promote.pl.

Indeed I can see the "# Check if the extension injection_points is available, as
it may be possible that this script is run with installcheck, where the module
would not be installed by default", in 041_checkpoint_at_promote.pl.

Thanks! I think that makes sense and will add it in the proposed patch (early
next week).

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com