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

[Ed W]

On 05/05/2011 09:44, Timo Sirainen wrote:
> 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.

Silly question, but I presume there is effectively no "negative caching"
from the OS for missing files, but presumably the OS would cache a zero
length file?

Would it be faster then to create 700 zero length acl files so that
these lookups will at least be returned from the OS cache instead of
causing IO seeks?  First open will be slow, but faster thereafter?

Just an idea?

Ed W