IMAP hibernate and scalability in general

[Mark Moseley]

On Thu, Apr 6, 2017 at 3:10 AM, Timo Sirainen <tss at iki.fi> wrote:

> On 6 Apr 2017, at 9.56, Christian Balzer <chibi at gol.com> wrote:
> >
> >> For no particular reason besides wanting to start conservatively, we've
> got
> >> client_limit set to 50 on the hibernate procs (with 1100 total
> hibernated
> >> connections on the box I'm looking at). At only a little over a meg
> each,
> >> I'm fine with those extra processes.
> >>
> > Yeah, but 50 would be a tad too conservative for our purposes here.
> > I'll keep an eye on it and see how it goes, first checkpoint would be at
> > 1k hibernated sessions. ^_^
>
> imap-hibernate processes are similar to imap-login processes in that they
> should be able to handle thousands or even tens of thousands of connections
> per process.
>

TL;DR: In a director/proxy setup, what's a good client_limit for
imap-login/pop3-login?

Would the same apply for imap-login when it's being used in proxy mode? I'm
moving us to a director setup (cf. my other email about director rings
getting wedged from a couple days ago) and, again, for the sake of starting
conservatively, I've got imap-login set to a client limit of 20, since I
figure that proxying is a lot more work than just doing IMAP logins. I'm
doing auth to mysql at both stages (at the proxy level and at the backend
level).

On a sample director box, I've got 10000 imap connections, varying from
50mbit/sec to the backends up to 200mbit/sec. About a third of the
connections are TLS, if that makes a diff. That's pretty normal from what
I've seen. The director servers are usually 90-95% idle.

Should I be able to handle a much higher client_limit for imap-login and
pop3-login than 20?