[Dovecot] high imap load on large folders

[Ingo Thierack]

Timo Sirainen schrieb:
> Is it actually the user CPU load or system CPU load? I'd think most of
> the time is spent on moving the new message to cur/ directory where
> there are the 58k messages.
>
>   
Most time on System.

Cpu(s): 10.3%us, 87.1%sy,  0.0%ni,  1.7%id,  0.0%wa,  0.3%hi,  0.7%si,  
0.0%st
Mem:    775148k total,   747620k used,    27528k free,   124464k buffers
Swap:   524280k total,       60k used,   524220k free,   186376k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  
COMMAND                                                              
10573 mailacce  19   0 20732  17m 5616 R 96.1  2.3   2:13.57 
imap                                                                  
10566 ingo      15   0  283m 273m 3544 S  1.3 36.2   3:33.49 
imapsync                                                              
10602 root      15   0  2364  956  756 R  0.7  0.1   0:00.44 top        

>> mail_nfs_storage: yes
>>     
>
> Disable this during the sync, it'll add delays. And if you don't have
> more than one NFS client accessing the same mailbox at the same time,
> you don't need it anyway.
>
> Also see if maildir_very_dirty_syncs=yes helps.
>
>   
set both parameter, no speedup. Im now on message 48000 and it takes 
around 5 seconds and more to transfer one
message.

>> strace output
>>     
>
> strace -tt would have been better, it would have shown timestamps then
> too. But it didn't look like it did anything unexpected.
>   
found attached a short strace with -tt ;-) is it normal, that he spent 
so much in entries like

08:48:30.167492 getdents64(7, /* 51 entries */, 4096) = 4080



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