Обсуждение: Teach isolation tester about injection points in background workers

I hit a limitation of the isolation tester when trying to reproduce a bug in
REPACK (CONCURRENTLY) [1]: it does not recognize that session is blocked due
to background worker waiting on an injection point. This patch tries to fix
that.

[1] https://www.postgresql.org/message-id/29157.1774029970%40localhost

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com

On Tue, Mar 24, 2026 at 04:25:47PM +0530, Srinath Reddy Sadipiralla wrote:
> +1. I was thinking can we move the logic of checking if bg workers are the
> reason of blocking the main backend
> inside pg_isolation_test_session_is_blocked
> to make it cleaner, and regarding "XXX Should we use a separate query for
> that?"
> i am confused here IIUC if we keep it as 1 query using UNION every time its
> for sure
> that both the queries will run, which can increase more execution time but
> less libpq/socket
> calls, but if we send as 2 queries if 1st query doesn't returns true we
> have to go and
> check the other query, so here if 2 queries ran then execution +
> libpq/socket calls overhead,
> so i am slightly inclined towards separating the queries , so that if 1st
> gets satisfied then
> we don't touch the 2nd query at all, please correct me if i am wrong here :)

Is there a benefit in this change outside the hypothetical REPACK
CONCURRENTLY?  Using separating queries may make more sense on
readability ground, at least.
--
Michael

Michael Paquier <michael@paquier.xyz> wrote:

> On Tue, Mar 24, 2026 at 04:25:47PM +0530, Srinath Reddy Sadipiralla wrote:
> > +1. I was thinking can we move the logic of checking if bg workers are the
> > reason of blocking the main backend
> > inside pg_isolation_test_session_is_blocked
> > to make it cleaner, and regarding "XXX Should we use a separate query for
> > that?"
> > i am confused here IIUC if we keep it as 1 query using UNION every time its
> > for sure
> > that both the queries will run, which can increase more execution time but
> > less libpq/socket
> > calls, but if we send as 2 queries if 1st query doesn't returns true we
> > have to go and
> > check the other query, so here if 2 queries ran then execution +
> > libpq/socket calls overhead,
> > so i am slightly inclined towards separating the queries , so that if 1st
> > gets satisfied then
> > we don't touch the 2nd query at all, please correct me if i am wrong here :)
>
> Is there a benefit in this change outside the hypothetical REPACK
> CONCURRENTLY?

Not at the moment. Perhaps I shouldn't pursue this patch until there's an
injection point in the tree that needs that.

> Using separating queries may make more sense on readability ground, at
> least.

Agreed.

--
Antonin Houska
Web: https://www.cybertec-postgresql.com