Horton

Re: [EXTERNAL] Re: Add non-blocking version of PQcancel

Jacob Champion <jacob.champion@enterprisedb.com>

View thread View on postgr.es
From: Jacob Champion <jacob.champion@enterprisedb.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
Cc: Jelte Fennema-Nio <postgres@jeltef.nl>, Tom Lane <tgl@sss.pgh.pa.us>, Denis Laxalde <denis.laxalde@dalibo.com>, vignesh C <vignesh21@gmail.com>, Thomas Munro <thomas.munro@gmail.com>, Greg Stark <stark@mit.edu>, "Gregory Stark (as CFM)" <stark.cfm@gmail.com>, Jelte Fennema <Jelte.Fennema@microsoft.com>, Daniel Gustafsson <daniel@yesql.se>, Peter Eisentraut <peter@eisentraut.org>, Andres Freund <andres@anarazel.de>, Justin Pryzby <pryzby@telsasoft.com>, Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2024-03-13T19:08:30Z
Lists: pgsql-hackers

Attachments

On Wed, Mar 13, 2024 at 12:01 PM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> On 2024-Mar-13, Jelte Fennema-Nio wrote:
> > Sadly I'm having a hard time reliably reproducing this race condition
> > locally. So it's hard to be sure what is happening here. Attached is a
> > patch with a wild guess as to what the issue might be (i.e. seeing an
> > outdated "active" state and thus passing the check even though the
> > query is not running yet)
>
> I tried leaving the original running in my laptop to see if I could
> reproduce it, but got no hits ... and we didn't get any other failures
> apart from the three ones already reported ... so it's not terribly high
> probability.  Anyway I pushed your patch now since the theory seems
> plausible; let's see if we still get the issue to reproduce.  If it
> does, we could make the script more verbose to hunt for further clues.

I hit this on my machine. With the attached diff I can reproduce
constantly (including with the most recent test patch); I think the
cancel must be arriving between the bind/execute steps?

Thanks,
--Jacob

Commits

  1. postgres_fdw: re-issue cancel requests a few times if necessary.

  2. Make postgres_fdw's query_cancel test less flaky.

  3. postgres_fdw: Split out the query_cancel test to its own file

  4. Fix copy-paste mistake in PQcancelCreate

  5. Make libpqsrv_cancel's return const char *, not char *

  6. Stabilize postgres_fdw test

  7. libpq-be-fe-helpers.h: wrap new cancel APIs

  8. dblink/isolationtester/fe_utils: Use new cancel API

  9. Put libpq_pipeline cancel test back

  10. Hopefully make libpq_pipeline's new cancel test more reliable

  11. libpq: Add encrypted and non-blocking query cancellation routines

  12. libpq: Move pg_cancel to fe-cancel.c

  13. Add tests for libpq query cancellation APIs

  14. Add missing connection statuses to docs

  15. libpq: Change some static functions to extern

  16. libpq: Add pqReleaseConnHosts function

  17. libpq: Move cancellation related functions to fe-cancel.c

  18. Make spelling of cancelled/cancellation consistent

  19. Be more wary about OpenSSL not setting errno on error.

  20. libpq: Use modern socket flags, if available.

  21. Drop test view when done with it.

  22. Doc: add some doco about using the libpq_pipeline test module.

  23. postgres_fdw: Allow cancellation of transaction control commands.