multiple messages per second to a single mailbox

[Chad M Stewart]

On Aug 12, 2015, at 11:58 AM, Daniel Tröder <troeder at univention.de> wrote:

> On 08/12/2015 17:19, Chad M Stewart wrote:
>> What I'm seeing is very high load on the system (40) and queues building on the Postfix side.
> High load means, that there are a lot of processes waiting to run. The
> most likely cause for this is not CPU consumption, but I/O wait.
> 
> Please run vmstat and iostat and post their output.

I was watching iostat and avg service times, and maybe once every 30-45 seconds I'd see times of 10ms, but otherwise it was below that.   I achieved the biggest impact by limiting the number of outbound connections from Postfix to Dovecot.  I limited Postfix to 5 connections, which means a total of 10 inbound LMTP to Dovecot.  Then I saw near 500 msgs per LMTP connection. 

I suspect the problem was a locking issue on the mailbox in question.  Too many simultaneous delivery attempts via too many LMTP sessions.

The backlog has cleared so I'm done troubleshooting for now.  If this happens again I'll resume looking into it more.  These are new servers so I'm tuning for the load, etc..


-Chad