[Dovecot] Significant performance problems

[Chris Hobbs]

  On 10/6/10 5:22 PM, Timo Sirainen wrote:
> Is the load CPU load or disk I/O load? If I/O load, what NFS 
> operations are peaking there, or all of them? Pretty graphs of nfsstat 
> output would be nice.
>
If I'm reading the output of our monitoring system correctly, the CPU is 
spending quite a bit of time in WAIT status, so I asuume that means it 
is IO bound?

After 19 minutes of uptime, nfsstat looks like (I'm not monitoring this 
[yet], so I don't have pretty graphs :/ ):

Client nfs v3:
null         getattr      setattr      lookup       access       readlink
0         0% 20389    15% 7615      5% 42198    31% 26896    20% 
58        0%
read         write        create       mkdir        symlink      mknod
6923      5% 5825      4% 4178      3% 29        0% 0         0% 
0         0%
remove       rmdir        rename       link         readdir      
readdirplus
2771      2% 0         0% 2500      1% 77        0% 7238      5% 
1428      1%
fsstat       fsinfo       pathconf     commit
3         0% 4         0% 2         0% 5690      4%

>> login_processes_count: 20
> Probably could use less then 20.
>
>> login_max_connections: 64
> And this could be higher. In general you should have maybe 1-2x the number of login processes than CPU cores.
Since this is in a virtual environment, I went ahead and ramped up the 
number of CPUs to 4, since I have the processors to spare.
>> mail_nfs_storage: yes
> You said you have only one server accessing mails. So set this to "no".
Done.
>> mail_location: maildir:~/Maildir:INDEX=/var/indexes/%u
> ..
>> namespace:
>>   type: shared
>>   separator: /
>>   prefix: shared/%%u/
>>   location: maildir:%%h/Maildir:INDEX=~/Maildir/shared/%%u
> The INDEX path here is wrong now.
Fixed - luckily most of our users don't share so this shouldn't have had 
a huge impact.
> Also you could try if maildir_very_dirty_syncs=yes is helpful.
Done.

Will report back tomorrow on how much these fixes help. Really 
appreciate the effort.

-- 
Chris Hobbs
Director, Technology
New Haven Unified School District

--
This message was scanned by ESVA and is believed to be clean.