RE: pgbench: option delaying queries till connections establishment?

From: Fabien COELHO <coelho(at)cri(dot)ensmp(dot)fr>
To: "kuroda(dot)hayato(at)fujitsu(dot)com" <kuroda(dot)hayato(at)fujitsu(dot)com>
Cc: Andres Freund <andres(at)anarazel(dot)de>, Daniel Gustafsson <daniel(at)yesql(dot)se>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: RE: pgbench: option delaying queries till connections establishment?
Date: 2020-11-07 17:33:27
Message-ID: alpine.DEB.2.22.394.2011062034410.1605435@pseudo
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Hello,

>> Indeed. I took your next patch with an added explanation. I'm unclear
>> whether proceeding makes much sense though, that is some thread would run
>> the test and other would have aborted. Hmmm.
>
> Your comment looks good, thanks. In the previous version pgbench starts
> benchmarking even if some connections fail. And users can notice the
> connection failure by stderr output. Hence the current specification may
> be enough.

Usually I run many pgbench through scripts, so I'm probably not there to
check a lone stderr failure at the beginning if performance figures are
actually reported.

> If you agree, please remove the following lines:
>
> ```
> + * It is unclear whether it is worth doing anything rather than
> + * coldly exiting with an error message.
> ```

I can remove the line, but I strongly believe that reporting performance
figures if some client connection failed thus the bench could not run as
prescribed is a bad behavior. The good news is that it is probably quite
unlikely. So I'd prefer to keep it and possibly submit a patch to change
the behavior.

>> ISTM that there is another patch in the queue which needs barriers to
>> delay some initialization so as to fix a corner case bug, in which case
>> the behavior would be mandatory. The current submission could add an
>> option to skip the barrier synchronization, but I'm not enthousiastic to
>> add an option and remove it shortly later.
>
> Could you tell me which patch you mention? Basically I agree what you say,
> but I want to check it.

Should be this one: https://commitfest.postgresql.org/30/2624/,

--
Fabien.

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