dovecot config for 1500 simultaneous connection

[KT Walrus]

> 1500 IMAP sessions will eat up about 3GB alone.

Are you saying that Dovecot needs 2MB of physical memory per IMAP session?

If I want to support a max 100,000 IMAP sessions per server, I should configure the server to have at least 200GBs of SWAP?

> On Feb 10, 2017, at 3:58 AM, Christian Balzer <chibi at gol.com> wrote:
> 
> 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/