Horde_Db + the injector solve this

DB::connect(), is indeed, not a singleton. Instead of using factory 
(which I'm guessing helps because the object isn't cached), we should 
probably cache the DB object so we don't need to keep recreating it.

This will be moot for Horde 4, though which will use Horde_Db.

I can't find any singleton functionality in DB.php. Perhaps you are 
talking about MDB2, but nag is still using the old DB interface.

DB::connect() is a singleton. Even if we create many Nag_Driver 
instances, DB::connect() should always return the same DB instance, 
and thus only use one db connection.

I added a print statement to connect and disconnect functions in 
DB/mysqli.php and called alarm cron job. It looks like DB connect 
get's called 2071 times (mostly from nag) without a single disconnect. 
And I would expect this as Nag::listAlarms gets called with a list of 
~2000 users and for each user it calls Nag_Driver::singleton($user). 
Since the $user is part of the instance signature, it creates a new 
Nag_Driver_sql instance for each user. And I don't see it trying to 
reuse existing connections in DB.php or DB/mysqli.php. I think you can 
reproduce this just by creating kronolith and nag alarms for a large 
number of users.

That doesn't make any sense because we use DB::connect() in the SQL 
driver which already is a singleton. Besides that we only have a 
single DB instance, the DB package also takes care of re-using open 
database connections.

It seems that using factory instead of singleton when $tasklist is set 
helps. Patch attached.

The cron job that should trigger scheduled alarms constantly fails 
with this error:

Nov 02 16:32:32 HORDE [error] [nag] The Tasks backend is not currently 
available: DB Error: connect failed [pid 19885 on line 228 of 
"/srv/webmail/www/lib/Horde/Alarm.php"]

It seems the problem is in the call to Nag::listAlarms. This function 
creates a new database connection for each storage instance and after 
a few hundred users database returns the error 'Too many connections'. 
Perhaps a single database connection could be used or old connections 
can be closed?