[horde] IMP IMAP DB Cache backend lifetime

[Joao S Veiga]

----- Message from Jens Wahnes <wahnes at uni-koeln.de> ---------

> Joao S Veiga wrote:
>> Even with very few users, without Frederico's suggestion the cache  
>> in the database will grow forever if not manually cleared (and the  
>> imp-query-imap-cache doesn't help much for old messages/metadata).
>>
>> So for the sql cache to properly work in any case, there should be  
>> a way to expire them, as he suggested.
>
> I agree that Horde should be able to clean up the mess it created.  
> ;-) But then, OTOH, the Horde configuration already comes with a big  
> "NOT RECOMMENDED" message regarding usage of a SQL database for  
> caching, so go figure.
>

There is a "NOT RECOMMENDED" for sql in the "Horde Cache"  
configuration option; is that what you mean? My "Horde Cache" uses the  
"File" driver, which is not marked "NOT RECOMMENDED".

But we're talking about the "IMP IMAP Cache", which can use the "Horde  
Cache" (not recommended), or hashtable/nosql/sql (recommended)  
according to imp/backends.php:

  *     - 'cache': Caching is enabled using the Horde cache (configured in
  *                horde/config/conf.php). It is recommended to use either
  *                'hashtable', 'nosql', or 'sql' instead, as these backends
  *                have better performance.
  *     - 'hashtable': Caching is enabled using the Horde HashTable driver
  *                    (configured in horde/config/conf.php).
  *                    The 'cache_lifetime' parameter (integer) can be
  *                    specified to define the lifetime of the cached message
  *                    data.
  *     - 'nosql': Caching is enabled using the Horde NoSQL database
  *                (configured in horde/config/conf.php).
  *     - 'sql': Caching is enabled using the Horde SQL database (configured in
  *              horde/config/conf.php).

Is this information incorrect, and the "IMP IMAP CACHE" shouldn't use  
sql either? In my set up (about 50 users, some with 2GB+ inboxes and  
20GB+ mailboxes) using MYSQL as the IMP IMAP Cache greatly improves  
the response, with not much impact in CPU usage (I do see mysql using  
a little CPU after I completely wipe out the cache but that's  
expected); but I'm comparing to not using caching at all.

Do you have a reason for not recommending sql for the "IMP IMAP  
Cache", or you thought we were referring to the "Horde Cache"?

Thanks,

Joao