Mongo Session Handler

A PHP session handler backed by MongoDB.

Installation

$ composer require altmetric/mongo-session-handler

Usage

<?php
use Monolog\Logger; // or any other PSR-3 compliant logger
use Altmetric\MongoSessionHandler;

$sessions = $mongoClient->someDB->sessions;
$logger = new Logger;
$handler = new MongoSessionHandler($sessions, $logger);

session_set_save_handler($handler);
session_set_cookie_params(0, '/', '.example.com', false, true);
session_name('my_session_name');
session_start();

Concurrency

As MongoDB prior to 3.0 does not support document level locking, this session handler operates on a principle of Last Write Wins.

If a user of a session causes two simultaneous writes then you may end up with the following situation:

1. Window A reads session value of ['foo' => 'bar'];
2. Window B reads session value of ['foo' => 'bar'];
3. Window B writes session value of ['foo' => 'baz'];
4. Window A writes session value of ['foo' => 'quux'].

The session will now contain ['foo' => 'quux'] as it was the last successful write. This may be surprising if you're trying to increment some value in a session as it is not locked during reads and writes:

1. Window A reads session value of ['count' => 0];
2. Window B reads session value of ['count' => 0];
3. Window B writes session value of ['count' => 1];
4. Window A writes session value of ['count' => 1].

Acknowledgements

• Nick Ilyin's php-mongo-session served as a valuable existing implementation of MongoDB-backed sessions in PHP.

License

Copyright © 2015 Altmetric LLP

Distributed under the MIT License.