[pgpool-general: 7813] Re: Error: sorry, too many clients

[michail alexakis]

Thanks Tatsuo

Is there any plan for this fix to be included in an upcoming Pgpool release
(I am running 4.2.4 from Alpine repositories)  ?
Or, do you consider this as too deployment-specific (and so I should create
a custom build from source of 4.2.4)?





On Mon, Oct 18, 2021 at 11:36 AM Tatsuo Ishii <ishii at sraoss.co.jp> wrote:

> >> In our environment:
> >> reserved_connections=0
> >> listen_backlog_multiplier=2
> >>
> >> So, if I understand correctly, we have 2 different problematic cases:
> >>
> >> (1) a client silently disappears (doesn't properly close the
> connection):
> >> In this case, setting `child_idle_limit` to a non-zero value (say 15min)
> >> could mitigate the problem, and eventually the child worker will again
> be
> >> available to handle an incoming connection.
> >>
> >> (2) a server-side child process crashes: In this case, Pgpool still
> keeps a
> >> dangling reference to this process, and if some client is routed there
> will
> >> get a "sorry, too many clients" error.
> >
> > Since the counter is shared by all process, any process could get a
> > "sorry..." error.
> >
> >> As for now, this problem cannot be
> >> mitigated unless the (parent) Pgpool process is restarted.
> >
> > Yes.
> >
> >> One more question:
> >> What can make a child process crash? (well, I mean, what are the most
> >> common reasons for that).
> >
> > Besides admin's mistake, probabbly the most case is OOM killer.
> >
> >> Does this crash leave any trace (that I should search for) in Pgpool's
> >> error log? Does parent Pgpool get notified on this (e.g. via waitpid or
> >> SIGCHLD)?
> >
> > Yes, Pgpool parent process should leave a log when catching SIGCHLD.
> > If I kill a child process using kill -9, I got following log:
> >
> > 2021-10-18 14:44:48.951: main pid 997555: LOG:  child process with pid:
> 997582 exits with status 9 by signal 9
> > 2021-10-18 14:44:48.952: main pid 997555: LOG:  fork a new child process
> with pid: 997609
>
> Actually if reserved_connections=0, then there's no need to manage the
> connection counter. So I have created a patch to eliminate the
> management part. You will never be troubled by the "sorry..."  error.
>
> If you like, please try attached patch.
> --
> Tatsuo Ishii
> SRA OSS, Inc. Japan
> English: http://www.sraoss.co.jp/index_en.php
> Japanese:http://www.sraoss.co.jp
>
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