Re: Restart pg_usleep when interrupted

Hi,

On Tue, Aug 13, 2024 at 04:30:46PM -0500, Nathan Bossart wrote:
> On Tue, Aug 13, 2024 at 01:12:30PM -0500, Imseih (AWS), Sami wrote:
> >> None of this seems intractable to me. 1 Hz seems like an entirely
> >> reasonable place to start, and it is very easy to change (or to even make
> >> configurable). pg_stat_progress_vacuum might show slightly old values in
> >> this column, but that should be easy enough to explain in the docs if we
> >> are really concerned about it. If other callers want to do something
> >> similar, maybe we should add a more generic implementation in
> >> backend_progress.c.
> >>
> > I don't know if I agree. Making vacuum sleep more robust to handle
> > interrupts seems like a cleaner general solution than to add
> > even more code to handle this case or have to explain the behavior of
> > cost delay instrumentation in docs.
>
> Another concern is the huge number of PqMsg_Progress messages sent by
> parallel workers with that approach. In Bertrand's tests, he was seeing
> nearly 350K interrupts for a ~19 minute vacuum (~300 interrupts per
> second). That seems a bit extreme to me. I don't see how anyone could
> possibly need stats about vacuum delays with that level of accuracy.
>

I gave it more thoughts and I don't think we have to choose between the two.
The 1 Hz approach reduces the number of interrupts and Sami's patch provides a
way to get "accurate" delay in case of interrupts. I think both have their own
benefit.

Regards,

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