On 6 Apr 2017, at 21.14, Mark Moseley moseleymark@gmail.com wrote:
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?
You should have the same number of imap-login processes as the number of CPU cores, so they can use all the available CPU without doing unnecessary context switches. The client_limit is then large enough to handle all the concurrent connections you need, but not so large that it would bring down the whole system if it actually happens.
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).
Proxying isn't doing any disk IO or any other blocking operations. There's no benefit to having more processes. The only theoretical advantage would be if some client could trigger a lot of CPU work and cause delays to handling other clients, but I don't think that's possible (unless somehow via OpenSSL but I'd guess that would be a bug in it then).
Should I be able to handle a much higher client_limit for imap-login and pop3-login than 20?
Yeah.