weakforced

[Mark Moseley]

On Thu, Aug 17, 2017 at 1:16 AM, Teemu Huovila <teemu.huovila at dovecot.fi>
wrote:

> Below is an answer by the current weakforced main developer. It overlaps
> partly with Samis answer.
>
> ---snip---
>  > Do you have any hints/tips/guidelines for things like sizing, both in a
> > per-server sense (memory, mostly) and in a cluster-sense (logins per sec
> ::
> > node ratio)? I'm curious too how large is quite large. Not looking for
> > details but just a ballpark figure. My largest install would have about 4
> > million mailboxes to handle, which I'm guessing falls well below 'quite
> > large'. Looking at stats, our peak would be around 2000 logins/sec.
> >
>
> So in terms of overall requests per second, on a 4 CPU server, latencies
> start to rise pretty quickly once you get to around 18K requests per
> second. Now, bearing in mind that each login from Dovecot could generate 2
> allow and 1 report requests, this leads to roughly 6K logins per second on
> a 4 CPU server.
>
> In terms of memory usage, the more the better obviously, but it depends on
> your policy and how many time windows you have. Most of our customers have
> 24GB+.
>
> > I'm also curious if -- assuming they're well north of 2000 logins/sec --
> > the replication protocol begins to overwhelm the daemon at very high
> > concurrency.
> >
> Eventually it will, but in tests it consumes a pretty tiny fraction of the
> overall CPU load compared to requests so it must be a pretty high limit.
> Also, if you don’t update the time windows DB in the allow function, then
> that doesn’t cause any replication. We’ve tested with three servers, each
> handling around 5-6000 logins/sec (i.e. 15-18K requests each) and the
> overall query rate was maintained.
>
> > Any rules of thumb on things like "For each additional 1000 logins/sec,
> add
> > another # to setNumSiblingThreads and another # to setNumWorkerThreads"
> > would be super appreciated too.
> >
>
> Actually the rule of thumb is more like:
>
> - WorkerThreads - Set to number of CPUs. Set number of LuaContexts to
> WorkerThreads + 2
> - SiblingThreads - Leave at 2 unless you see issues.
>
> > Thanks! And again, feel free to point me elsewhere if there's a better
> > place to ask.
> Free free to ask questions using the weakforced issues on GitHub.
>
> > For a young project, the docs are actually quite good.
>
> Thanks, that’s appreciated - we try to keep them up to date and
> comprehensive.
>
>
>

Wow, wow, wow. Thanks so much to all three of you guys for such detailed
answers. That's absolutely perfect info and just what I was looking for.