[Dovecot] severe performance problem (mail cache related?)

[Jeff A. Earickson]

On Fri, 16 Feb 2007, Timo Sirainen wrote:

> Date: Fri, 16 Feb 2007 13:39:33 +0200
> From: Timo Sirainen <tss at iki.fi>
> To: Dan Price <dp at eng.sun.com>
> Cc: dovecot at dovecot.org
> Subject: Re: [Dovecot] severe performance problem (mail cache related?)
> 
> On Fri, 2007-02-16 at 03:29 -0800, Dan Price wrote:
>>> Yes, and it's done as long as you don't have mmap_disable=yes. Hmm.
>>> Weren't you using ZFS directly? Why are you using mmap_disable=yes? :)
>>> Its main purpose is to make indexes work in NFS.
>>
>> Well there you go, I'm a dope.  I think I set mmap_disable=yes because I
>> was seeing strange things happening where there would be thousands
>> (millions?) of madvise(DONTNEED) calls-- seemingly forever in a loop.  I
>> have not yet tracked that problem down-- next time I see it, I will
>> make sure to get to the bottom of it.
>
> Actually the only place where madvise(MADV_DONTNEED) is called is in the
> file-cache code which is used only with mmap_disable=yes.
>
> There are madvise(MADV_SEQUENTIAL) calls with mmap_disable=no though.
>
>
Dan,

    Could you give us other Sun users a few details of your setup, so we
can avoid this hole?  I am running rc22 on a T2000, Solaris 10 11/06
plus (mostly) current patches, ZFS version 3 for my user homedirs (where
cache files and folders go), INBOXes NFS mounted from another Sun S10
box (NFS version 4).  I have never touched any of the mmap related settings
in dovecot.conf.  The whole thing works beautifully for 3000 users.
The T2000 never breaks a sweat.  The users are happy.

Jeff Earickson
Colby College