Re: Allow non-superuser to cancel superuser tasks.

From: Nathan Bossart <nathandbossart(at)gmail(dot)com>
To: Michael Paquier <michael(at)paquier(dot)xyz>
Cc: "Andrey M(dot) Borodin" <x4mmm(at)yandex-team(dot)ru>, Kirill Reshke <reshkekirill(at)gmail(dot)com>, "Leung, Anthony" <antholeu(at)amazon(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Allow non-superuser to cancel superuser tasks.
Date: 2024-07-12 01:50:57
Message-ID: ZpCMAewARMJQSbKa@nathan
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On Wed, Jul 10, 2024 at 02:14:55PM +0900, Michael Paquier wrote:
> +# Only non-superuser roles granted pg_signal_autovacuum_worker are allowed
> +# to signal autovacuum workers. This test uses an injection point located
> +# at the beginning of the autovacuum worker startup.

nitpick: Superuser roles are also allowed to signal autovacuum workers.
Maybe this should read "Only roles with privileges of..."

> +# Create some content and set an aggressive autovacuum.
> +$node->safe_psql(
> + 'postgres', qq(
> + CREATE TABLE tab_int(i int);
> + ALTER TABLE tab_int SET (autovacuum_vacuum_cost_limit = 1);
> + ALTER TABLE tab_int SET (autovacuum_vacuum_cost_delay = 100);
> +));
> +
> +$node->safe_psql(
> + 'postgres', qq(
> + INSERT INTO tab_int VALUES(1);
> +));
> +
> +# Wait until an autovacuum worker starts.
> +$node->wait_for_event('autovacuum worker', 'autovacuum-worker-start');

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?

> +# Wait for the autovacuum worker to exit before scanning the logs.
> +$node->poll_query_until('postgres',
> + "SELECT count(*) = 0 FROM pg_stat_activity "
> + . "WHERE pid = $av_pid AND backend_type = 'autovacuum worker';");

WFM. Even if the PID is quickly reused, this should work. We just might
end up waiting a little longer.

Is it worth testing cancellation, too?

--
nathan

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