[Dovecot] Slow DNS warnings (proxy/auth)

[Timo Sirainen]

On 26.4.2013, at 11.57, Christian Balzer <chibi at gol.com> wrote:

> Apr 25 17:19:09 pp11 dovecot: auth: Warning: proxy(redacted at gol.com,xx.xx.xx.xx,<26hUEivbfQBlMrMS>): DNS lookup for mb04.dentaku.gol.com took 5.002 s
> ---
> 
> Now this machine at that time was handling a load of about 2 logins per
> second, about 20% of what it previously handled with perdition w/o a
> hiccup.
> It also runs a local caching nameserver and the A record for the mailbox
> server in question was most definitely cached at the time (verified via
> TTL). 
> The machine in question was very bored and certainly capable of handling
> hundreds if not thousands of DNS queries per second at that moment.
> 
> In short, I can't see any reason how the lookup could have taken so long, so my guess is there are some issues with the dns-helper (locking, stepping on each others feet, not being spawned fast enough) causing this.

No idea.

> Some general remarks, dovecot as proxy feels "heavier" than perdition. 
> 
> In the CPU area that's probably a more subjective impression, because all
> the little helper processes make it clear what's going on where. 
> Though the "config" process being rather active is something that perdition
> definitely doesn't do, it reads the config once at start time and that's
> it. 
> All the IPC and central processes of course also make dovecot rather
> file handle hungry.
> 
> Memory wise it's about 35% bigger than perdition and that's not subjective
> at all. ^o^
> About one MB per proxy process/connection for dovecot in my case.
> Caveat emptor. ^o^

You could also switch to high-performance mode: http://wiki2.dovecot.org/LoginProcess