Re: pgbnech: allow to cancel queries during benchmark

On Fri, 19 Jan 2024 17:46:03 +0900 (JST)
Tatsuo Ishii <ishii(at)sraoss(dot)co(dot)jp> wrote:

> >> +/* send cancel requests to all connections */
> >> +static void
> >> +cancel_all()
> >> +{
> >> + for (int i = 0; i < nclients; i++)
> >> + {
> >> + char errbuf[1];
> >> + if (client_states[i].cancel != NULL)
> >> + (void) PQcancel(client_states[i].cancel, errbuf, sizeof(errbuf));
> >> + }
> >> +}
> >> +
> >>
> >> Why in case of errors from PQCancel the error message is neglected? I
> >> think it's better to print out the error message in case of error.
> >
> > Is the message useful for pgbench users? I saw the error is ignored
> > in pg_dump, for example in bin/pg_dump/parallel.c
>
> I think the situation is different from pg_dump. Unlike pg_dump, if
> PQcancel does not work, users can fix the problem by using
> pg_terminate_backend or kill command. In order to make this work, an
> appropriate error message is essential.

Makes sense. I fixed to emit an error message when PQcancel fails.

Also, I added some comments about the signal handling on Windows
to explain why the different way than non-Windows is required;

+ * On Windows, a callback function is set in which query cancel requests
+ * are sent to all benchmark queries running in the backend. This is
+ * required because all threads running queries continue to run without
+ * interrupted even when the signal is received.
+ *

Attached is the updated patch, v6.

> Best reagards,
> --
> Tatsuo Ishii
> SRA OSS LLC
> English: http://www.sraoss.co.jp/index_en/
> Japanese:http://www.sraoss.co.jp
>
>

--
Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp>