extremely poor performance with many maiboxes for 'list "" *'

[Rob Mueller]

>I manage a single-instance server running v2.2.12 with a reasonably
> large number of mailboxes, using "mboxlist_db: flat":

Why are you using "flat"? The flat db implementation is pretty basic/kludgy 
and not designed for large database files. I bet it's doing something stupid 
like re-reading the file from scratch for each record or something like that 
(I've seen it try to rewrite a file on every record when coverting from 
skiplist -> flat)

Convert it to a skiplist and use that instead, much, much better performance 
with up to millions of mailboxes.

http://cyrusimap.web.cmu.edu/twiki/bin/view/Cyrus/WhatDatabaseBackend

Rob