[pgpool-general: 7811] Re: Error: sorry, too many clients

[Tatsuo Ishii]

>> 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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