[Dovecot] lmtp-proxying in 2.1 slower than in 2.0.14 ?

[Timo Sirainen]

On 5.2.2013, at 11.57, Jan-Frode Myklebust <janfrode at tanso.net> wrote:

> I think there must be some bug I'm hitting here. One of my directors
> is still running with "client_limit = 1, process_limit = 100" for the
> lmtp service, and now it's logging:
> 
>   master: Warning: service(lmtp): process_limit (100) reached, client
> connections are being dropped
> 
> Checking "sudo netstat -anp|grep ":24 " I see 287 ports in TIME_WAIT,
> one in CLOSE_WAIT and the listening "0.0.0.0:24". No active
> connections. There are 100 lmtp-processes running.

Sounds like the LMTP processes are hanging for some reason.. http://hg.dovecot.org/dovecot-2.1/rev/63117ab893dc might show something interesting, although I'm pretty sure it will just say that the processes are hanging in DATA command.

Other interesting things to check:

gdb -p <pid of lmtp process>
bt full

strace -tt -p <pid of lmtp process> (for a few seconds to see if anything is happening)

If lmtp proxy is hanging, it should have a timeout (default 30 secs) and it should log about it if it triggers. (Although maybe not to error log.)

> When trying to
> connect to the lmtp-port I immediately get dropped:
> 
> $ telnet localhost 24
> Trying 127.0.0.1...
> Connected to localhost.localdomain (127.0.0.1).
> Escape character is '^]'.
> Connection closed by foreign host.

This happens when the master process notices that all the service processes are full.

> Is there maybe some counter that's getting out of sync, or some back
> off penalty algorithm that kicks in when it first hit the process
> limit ?

Shouldn't be, but the proctitle patch should make it clearer. Strange anyway, I haven't heard of anything like this happening before.