[Dovecot] POP3 error

[Thierry de Montaudry]

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.