dovecot config for 1500 simultaneous connection

[Christian Balzer]

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/