[Dovecot] Dovecot very slow on a mailbox with > 700 IMAP Folders

[Stan Hoeppner]

On 5/10/2011 1:19 AM, Becker, Ronny wrote:
> Am 05.05.2011 10:44, schrieb Timo Sirainen:
>> On 5.5.2011, at 10.19, Timo Sirainen wrote:
>>
>>>> I did some debugging with strace, too. It's about 22MB only for
>>>> running the lsub command !?
>>> Run it with strace -tt and send me the output compressed?
>> Ah, you have ACLs enabled. With ACLs it's looking up dovecot-acl file
>> from each folder before returning it. This shouldn't be necessary with
>> LSUB I think. I suppose some kind of an ACL cache could be a good idea
>> some day too. And maybe a setting not to bother looking up ACLs for
>> mailboxes in private namespaces.
>>
>> I'll try to do something about those within a few days..
>>
> Someone told me, that this problem should not happen when
> acl_shared_dict is used. But this was enabled in our setup. Is there any
> other workaround to use ACLs with such a large number of folders?!

In the absence of Timo producing the patches he mentioned in short order...

Install this 3.5" Vertex2 120GB SATA II SSD for less than $250 USD 
incl/shipping:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227590
(If you're shy of using a 'consumer' marketed unit, buy the 64GB Intel 
SLC for ~$700)

This Vertex2 will give you 50,000 random write IOPS (~same for read) 
with 0.1ms seek latency, approximately 3x the IOPS of a $75k 60x15k SAS 
drive Nexsan e60 FC SAN array and 50x lower seek latency--but with only 
1/300th the capacity.

Format with EXT3/4, and simply move your problem user's entire mail 
directory to the SSD and change his mail location setting.  Problem 
solved instantly, with authority.  As you should have ~100GB of space 
left on the SSD after moving him/her over, move all user indexes to the 
SSD as well.  This will yield an incredible speed boost for all users, 
and prevent any 'jealously' politics when word spreads of 'Bob' getting 
his own super-duper fast drive in the server.

-- 
Stan