1. Concurrency : Locking is managed by MongoDB's internal WiredTiger storage engine hence no need of PHP level locking. more read
2. PHP Garbage Collector : instead of leting PHP GC to clean expired sessions, MongoDB's TTL based collection do this job to clean expired session hence less responsibility on PHP making code execution faster. more read

1. Make sure you have PECL MongoDB driver installed and enabled in PHP ini file. Please check https://pecl.php.net/package/mongodb

1. Download the repo

2. put Session_mongo_driver.php inside folder YOUR_PROJECT_FOLDER/application/libraries/Session/drivers folder, if you didn't have those folders then please do create. (Pay attention to folder name, its case sensitive)

3. Selecting correct driver in YOUR_PROJECT_FOLDER/application/config.php file, find variable name $config['sess_driver'] and set its value mongo.

4. Applying MongoDB login details in YOUR_PROJECT_FOLDER/application/config.php file, find variable name $config['sess_save_path'] and set its value exactly like below (don't forgot to change the value with correct one)

$config['sess_save_path'] = 'mongodb://USER_ID:PASSWORD@HOST:PORT/DATABASE_NAME|DATABASE_NAME|COLLECTION_NAME';

e.g

$config['sess_save_path'] = 'mongodb://session_user:123456@localhost:27017/my_app|my_app|sessions_collection';

5. Set TTL based indexed in your MongoDB's Collection. Default value is 1 hour, you can set whatever you want in below query

db.YOUR_COLELCTION_NAME.createIndex( { "timestamp": 1 }, { expireAfterSeconds: 3600 } )

Codeiginiter's standard functions $this->session-> to access session data, driver will take care the rest.

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