What could stop Zend_Session::setSaveHandler from working - php

Question

I'm working a reasonably large zf1 project with multiple modules. We need to store the session state in the database for a new deployment. After a quick google we came across Zend_Session_SaveHandler_DbTable and followed the simple example (almost exactly) at http://framework.zend.com/manual/1.12/en/zend.session.savehandler.dbtable.html . I've placed the code in our application/Bootstrap.php and have checked it runs. However the database table is never populated with session data.
I thought something would be overriding the Zend_Session::setSaveHandler later in the code base but I can not find any other calls to that or Zend_Session::start();
Any suggestions on what might be wrong or how to investigate further?
edit with updated information:
here's how the relevant section of the bootstrap appears, currently just set up for dev mode.
protected function _initSessionDB()
{
$db = Zend_Db::factory('Pdo_Mysql', array(
'host' =>'localhost',
'username' => '****',
'password' => '****',
'dbname' => '****'
));
Zend_Db_Table_Abstract::setDefaultAdapter($db);
$config = array(
'name' => 'session_state',
'primary' => 'id',
'modifiedColumn' => 'modified',
'dataColumn' => 'data',
'lifetimeColumn' => 'lifetime'
);
Zend_Session::setSaveHandler(new Zend_Session_SaveHandler_DbTable($config));
Zend_Session::start();
}
and the database has
mysql> explain session_state;
+----------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------+----------+------+-----+---------+-------+
| id | char(32) | YES | | NULL | |
| modified | int(11) | YES | | NULL | |
| lifetime | int(11) | YES | | NULL | |
| data | text | YES | | NULL | |
+----------+----------+------+-----+---------+-------+
4 rows in set (0.00 sec)

Answer 1

So turns out that the application I was working on sets up the FlashMessenger controller helper in the application/Bootstrap.
protected function _initAutoload()
{
Zend_Controller_Action_HelperBroker::addHelper(
new Zend_Controller_Action_Helper_FlashMessenger());
}
The FlashMessenger action helper makes its own call to Zend_Session::start(); which seems to take priority over any later calls.
Simple solution is to add a $this->bootstrap('sessionDB'); call before the FlashMessenger is created. for example,
protected function initFlashMessenger()
{
$this->bootstrap('sessionDB');
if (APPLICATION_ENV != 'testing')
Zend_Controller_Action_HelperBroker::addHelper(
new Zend_Controller_Action_Helper_FlashMessenger());
}
A better solution would be to not create the FlashMessenger in the bootstrap at all and just create it within controllers or appropriate base controller.