dovecot config for 1500 simultaneous connection

[Rajesh M]

----- Original Message -----
From: Christian Balzer [mailto:chibi at gol.com]
To: dovecot at dovecot.org
Cc: 24x7server at 24x7server.net
Sent: Fri, 10 Feb 2017 17:58:58 +0900
Subject: 

On Fri, 10 Feb 2017 01:13:20 +0530 Rajesh M wrote:

> hello
> 
> could somebody with experience let me know the dovecot config file settings to handle around 1500 simultaneous connections over pop3 and 1500 connection over imap simultaneously.
> 

Be very precise here, you expect to see 1500 as the result of 
"doveadm who |grep pop3 |wc -l"?

Because that implies an ungodly number of POP3 connects per second, given
the typically short duration of these.

1500 IMAP connections (note that frequently a client will have more than
the INBOX open and thus have more than one session and thus process on the
server) are a much easier proposition, provided they are of the typical
long lasting type.

So can you put a number to your expected logins per second (both protocols)?

> my server
> 
> server configuration
> hex core processor, 16 gb ram 1 X 600 gb 15 k rpm for main drive and 2 X 2000 
> gb hdd for data (No raid)
> 
No RAID and no other replication like DRBD?
Why would you even bother?

How many users/mailboxes in total with what quota? 

1500 IMAP sessions will eat up about 3GB alone.
You will want more memory, simply to keep all relevant SLAB bits (inodes,
dentries) in RAM. 

If you really have several hundreds logins/s,  you're facing several
bottlenecks:
1. Login processes themselves (easily fixed by high performance mode)
2. Auth processes (that will depend on your backends, method mostly)
3. Dovecot master process (spawning mail processes)

The later is a single-threaded process, so it will benefit from a faster
CPU core.
It can be dramatically improved by enabling process re-usage, see:
http://wiki.dovecot.org/PerformanceTuning

However that also means more memory usage.



Christian

> 
> thanks
> rajesh
> 

[snip]
-- 
Christian Balzer        Network/Systems Engineer                
chibi at gol.com   	Global OnLine Japan/Rakuten Communications
http://www.gol.com/


thanks christian

during peak times here are the results for connections

[root at ns1 domains]# doveadm who |grep imap |wc -l
username                # proto (pids)                             (ips)
631
[root at ns1 domains]# doveadm who |grep pop3 |wc -l
username                # proto (pids)                          (ips)
233


could you please guide me concerning the dovecot config files settings to handle the above 631 imap and 233 pop connections.

number of mailboxes is around 4000 -- some users would consume 25 GB while others would be just around 10 MB

this is a hex core machine with hyperthreading -- so 12 cores

[root at ns1 domains]# iostat
Linux 2.6.32-431.29.2.el6.x86_64 (ns1.bizmailserver.net)        02/10/2017      _x86_64_        (12 CPU)

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
                   2.67       0.00    0.65           3.43        0.00       93.25

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sdd              44.95      1094.25       765.10  720884842  504041712
sdc               1.92        32.15         0.03   21178186      21248
sdb              34.71      1377.37       625.54  907398402  412102224
sda              49.88       124.29      2587.32   81879548 1704506408



thanks
rajesh