[imp] up-imapproxy and select caching

[Michael M Slusarz]

Quoting Aria Bamdad <ARIA at biostat.bsc.gwu.edu>:

> Hi,
>
> I have an installation of Horde Groupware webmail Edition 1.2.2, with
> IMP 4.3.3 and PHP 5.2.5.
>
> The Horde Performance Guide
>
> http://www.horde.org/horde/docs/?f=PERFORMANCE.html
>
> under IMAP tuning says that if using up-imapproxy, "make sure SELECT
> caching is turned off".
>
> When I do this, I get poor performance because the up-imapproxy unselects
> the mailbox after every single transaction, so the entire mailbox index
> structure for a given mailbox has to be reloaded for every single
> transaction.  This is something that the developer of up-imapproxy
> is aware of.

This should really not be a problem with any recent IMAP server - on  
servers like dovecot and cyrus, this should be instantaneous (since  
this information is cached server side).  If you are seeing "poor  
performance" on SELECT/EXAMINE commands, you *really* need to switch  
IMAP servers.

> When I turn on select caching, IMP performance is excellent.  My question
> is why does the above Horde document say to turn off the select caching?
> Does turning on select caching cause a problem?

Oh yes.  Multiple concurrent accesses to a mailbox is bad news with  
select caching.  An APPEND to the current mailbox breaks caching.   
IIRC, new messages delivered to the mailbox aren't recognized.  These  
are all Bad Things.

Don't use it.  IMAP caching needs to be done at the client level, not  
the proxy level.

michael

-- 
___________________________________
Michael Slusarz [slusarz at horde.org]