Re: Allow non-superuser to cancel superuser tasks.

On Fri, Jul 12, 2024 at 02:21:09PM +0900, Michael Paquier wrote:
> On Thu, Jul 11, 2024 at 08:50:57PM -0500, Nathan Bossart wrote:
>> I'm not following how this is guaranteed to trigger an autovacuum quickly.
>> Shouldn't we set autovacuum_vacuum_insert_threshold to 1 so that it is
>> eligible for autovacuum?
> 
> You are right, this is not going to influence a faster startup of a
> worker, so we could remove that entirely.  On closer look, the main
> bottlebeck is that the test is spending a lot of time waiting on the
> naptime even if we are using the minimum value of 1s, as the scan of
> pg_stat_activity checking for workers keeps looping.

I suppose it would be silly to allow even lower values for
autovacuum_naptime (e.g., by moving it to ConfigureNamesReal and setting
the minimum to 0.1).

> I have one trick in my sleeve for this one to make the launcher more
> responsive in checking the timestamps of the database list.  That's
> not perfect, but it reduces the wait behind the worker startups by
> 400ms (1s previously as of the naptime, 600ms now) with a reload to
> set the launcher's latch after the injection point has been attached.
> The difference in runtime is noticeable.

That's a neat trick.  I was confused why this test generates an autovacuum
worker at all, but I now see that you are pausing it before we even gather
the list of tables that need to be vacuumed.

>> Is it worth testing cancellation, too?
> 
> The point is to check after pg_signal_backend, so I am not sure it is
> worth the extra cycles for the cancellation.

Agreed.

> What do you think?

Looks reasonable to me.

-- 
nathan