session is storing to file rather than database - php

Question

Thanks for your help in advance.
I have just migrated my webserver from apache to nginx. Session information was happily being stored in the database previously, now for some reason they are writing to the /tmp directory.
Here is the code to set the session handler:
session_write_close();
$sess = new sessionHandler();
session_set_save_handler(array($sess, 'open'),
array($sess, 'close'),
array($sess, 'read'),
array($sess, 'write'),
array($sess, 'destroy'),
array($sess, 'gc'));
register_shutdown_function('session_write_close');
session_start();
$cookieLifetime = 365 * 24 * 60 * 60;
setcookie(session_name(),session_id(),time()+$cookieLifetime);
and here is the session handler class:
class appSessionHandler {
private $db;
public function open($save_path, $session_name) {
$this -> db = new appSql();
return true;
}
public function close() {
$this -> db -> close();
}
function read($id) {
// Create Memcache Class
$memcache = new memcacher();
var_dump('123');
// Check Memcache
$memcache->key = 'session-' . $id;
$memcache->get();
// If results is in memcache
if ($memcache->result != false){
$res = $memcache->result;
return $res;
}
// Else get the result from sql and update cache
else{
$this->open();
$this->db->sqlQuery = "SELECT data FROM session WHERE id = :id";
$this->db->params = array('id' => $id);
$res = $this->db->sqlQuery();
if (count($res) >= 1){
$memcache->input = $res[0]->data;
$memcache->duration = 2000;
$memcache->set();
return $res[0]->data;
}
return '';
}
}
function write($id, $data) {
$access = time();
$this->open();
// Create Memcache Class
$memcache = new memcacher();
// Check Memcache
$memcache->key = 'session-' . $id;
$memcache->input = $data;
$memcache->duration = 2000;
$memcache->set();
$this->db->sqlQuery = "REPLACE INTO session VALUES (:id, :access, :data)";
$this->db->params = array('id' => $id, 'access' => $access, 'data' => $data);
return $this->db->sqlQuery();
}
function destroy($id) {
// Delete From SQL
$this->open();
$this->db->sqlQuery = "DELETE FROM session WHERE id = :id";
$this->db->params = array('id' => $id);
// Create Memcache Class
$memcache = new memcacher();
// Check Memcache
$memcache->key = 'session-' . $id;
$memcache->delete();
return $this->db->sqlQuery();
}
function gc($max) {
$old = time() - $max;
$this->open();
$this->db->sqlQuery = "DELETE FROM session WHERE access < :old";
$this->db->params = array('old' => $old);
return $this->db->sqlQuery();
}
public function killUserSession($username){
$this->open();
$this->db->sqlQuery = "delete from session where data like('%userID|s:%\" :username %\";first_name|s:%')";
$this->db->params = array('username' => $username);
$this->db->sqlQuery();
}
}
I am lost!