Scaling to 10 Million IMAP sessions on a single server

[Sami Ketola]

> On 22 Feb 2017, at 6.12, Christian Balzer <chibi at gol.com> wrote:
> 
> On Tue, 21 Feb 2017 09:49:39 -0500 KT Walrus wrote:
> 
>> I just read this blog: https://mrotaru.wordpress.com/2013/10/10/scaling-to-12-million-concurrent-connections-how-migratorydata-did-it/ <https://mrotaru.wordpress.com/2013/10/10/scaling-to-12-million-concurrent-connections-how-migratorydata-did-it/> about scaling to 12 Million Concurrent Connections on a single server and it got me thinking.
>> 
> 
> While that's a nice article, nothing in it was news to me or particular
> complex when one does large scale stuff, like Ceph for example. 
> 
>> Would it be possible to scale Dovecot IMAP server to 10 Million IMAP sessions on a single server?
>> 
> I'm sure Timo's answer will (or would, if he could be bothered) be along
> the lines of: 
> "Sure, if you give me all your gold and then some for a complete rewrite
> of, well, everything”.


Well. The current bottleneck in achieving that would probably be the memory 
amount required. With 12M active sessions (non-hibernated) the memory requirement 
for that 12M active user single instance server would be huge. Approximately 10TB. 

If 12M active sessions is the target then the architecture of one user per imap process
needs to be abandoned.

Sami