[Dovecot] POP3 error
Thierry de Montaudry
thierry at mailhub.co.za
Tue Mar 8 17:40:12 EET 2011
On 08 Mar 2011, at 13:24, Chris Wilson wrote:
> Hi Thierry,
>
> On Tue, 8 Mar 2011, Thierry de Montaudry wrote:
>> On 07 Mar 2011, at 19:15, Timo Sirainen wrote:
>>> On Mon, 2011-03-07 at 19:03 +0200, Thierry de Montaudry wrote:
>>>>>>>>> Mar 7 11:19:51 xxx dovecot: pop3-login: Error: net_connect_unix(pop3) failed: Resource temporarily unavailable
>>>>> ..
>>>> As it is happening at least once a day, is there anything I can do to
>>>> trace it? and whatever I'll do, will it slow down those machines?
>>>
>>> Set verbose_proctitle=yes (won't slow down) and get list of all
>>> Dovecot processes when it happens. And check how much user and system
>>> CPU it's using and what the load is.
>>
>> Got the same problem this morning, here is the CPU usage and ps aux for
>> dovecot. plus the different error I could pick up in the log, most of
>> them are repeated a couple of times.
>>
>> I suspect it a problem with system resources, but can find any message
>> to tell me what. Mail are stored on 17 NFS servers (CentOS), plus 3
>> servers for indexes only.
>>
>> CPU load is very high, but mainly from httpd running our webmail
>> interface, which uses the local imap server.
> [...]
>> top - 11:10:14 up 14 days, 12:04, 2 users, load average: 55.04, 29.13, 14.55
>> Tasks: 474 total, 60 running, 414 sleeping, 0 stopped, 0 zombie
>> Cpu(s): 99.6%us, 0.3%sy, 0.0%ni, 0.0%id, 0.0%wa, 0.0%hi, 0.1%si, 0.0%st
>> Mem: 16439812k total, 16353268k used, 86544k free, 33268k buffers
>> Swap: 4192956k total, 140k used, 4192816k free, 8228744k cached
>
> You're lucky this server is still alive and that you could even run top
> and ps on it.
>
> There's nothing to debug in dovecot here. Your server is overloaded by
> about 55 times. Buy 55 times as many servers or do something about your
> webmail interface (maybe a separate webmail cluster).
>
> Cheers, Chris.
>
As you can see the numbers (55.04, 29.13, 14.55) the load was busy getting higher when I took this snapshot and this was not a normal situation. Usually this machine's load is only between 1 and 4, which is quite ok for a quad core. It only happens when dovecot start generating errors, and pop3, imap and http get stuck. It went up to 200, and I was still able to stop web and mail daemons, then restart them, and everything was back to normal.
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