Horrible performance in Zend Db PDO_sqlite inserting and updating queries

I'm having some serious sqlite database performance issues. I use it to store a small amount of data, which should be very fast, but for some reason too long. First of all, I create a Zend_Db object with a static factory method:

$this->db = Zend_Db::factory('PDO_SQLITE', $params);

Then I run a simple query:

$this->db->query($q)

And here comes the time from the magazines:

2012-04-26 13: 08: 06.752855: UPDATE sessionSET value= '542M', timeStamp= '1335438486', type = '999', ip= '62 .21.30.77 'WHERE name=' code1 'AND id_session =' 8fac3359f5c352b64a807745667746ce ' 0.1453s

0.1453s seems really huge for such a simple request. Moreover, sometimes such requests last for almost 0.5 s.

Indexes created in the database.

Any ideas what could be the problem? Or is this how Zend_Db works with sqlite?