How to set the redis session driver?

On a site I expierence a lot of

","exception":"[object] (Illuminate\Database\QueryException(code: HY000): SQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded; try restarting transaction (SQL: update `sessions` set `payload` = payload `last_activity` = 1520538614, `user_id` = USERID, `ip_address` = IP_ADDRESS, `user_agent` = USERAGENT where `id` = SESSION_ID) at /var/www/html/laravel/vendor/laravel/framework/src/Illuminate/Database/Connection.php:664, Doctrine\DBAL\Driver\PDOException(code: HY000): SQLSTATE[HY000]: General error: 1205 Lock wait timeout exceeded; try restarting transaction at /var/www/html/laravel/vendor/doctrine/dbal/lib/Doctrine/DBA

At time of writing there are about 76k active sessions in the database.

I read a lot of articles on stackoverflow and elsewhere but couldn't find a solution for it. So I thought It would be good to store the sessions in the faster Redis Server but I won't get it to configure it correctly.

In my .env file I changed from database to SESSIONDRIVER=redis. But how do i specify a redis connection in the session.php file?

My database.php looks like:

<?php

return [

    /*
    |--------------------------------------------------------------------------
    | Default Database Connection Name
    |--------------------------------------------------------------------------
    |
    | Here you may specify which of the database connections below you wish
    | to use as your default connection for all database work. Of course
    | you may use many connections at once using the Database library.
    |
    */

    'default' => env('DB_CONNECTION', 'mysql'),



    'connections' => [

        'sqlite' => [
            'driver' => 'sqlite',
            'database' => env('DB_DATABASE', database_path('database.sqlite')),
            'prefix' => '',
        ],

        'mysql' => [
            'driver' => 'mysql',
            'host' => env('DB_HOST', '127.0.0.1'),
            'port' => env('DB_PORT', '3306'),
            'database' => env('DB_DATABASE', 'hds'),
            'username' => env('DB_USERNAME', 'root'),
            'password' => env('DB_PASSWORD', ''),
            'unix_socket' => env('DB_SOCKET', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => true,
            'engine' => 'InnoDB',
        ],

        'pgsql' => [
            'driver' => 'pgsql',
            'host' => env('DB_HOST', '127.0.0.1'),
            'port' => env('DB_PORT', '5432'),
            'database' => env('DB_DATABASE', 'forge'),
            'username' => env('DB_USERNAME', 'forge'),
            'password' => env('DB_PASSWORD', ''),
            'charset' => 'utf8',
            'prefix' => '',
            'schema' => 'public',
            'sslmode' => 'prefer',
        ],

        'sqlsrv' => [
            'driver' => 'sqlsrv',
            'host' => env('DB_HOST', 'localhost'),
            'port' => env('DB_PORT', '1433'),
            'database' => env('DB_DATABASE', 'forge'),
            'username' => env('DB_USERNAME', 'forge'),
            'password' => env('DB_PASSWORD', ''),
            'charset' => 'utf8',
            'prefix' => '',
        ],

    ],


    /*
    |--------------------------------------------------------------------------
    | Redis Databases
    |--------------------------------------------------------------------------
    |
    | Redis is an open source, fast, and advanced key-value store that also
    | provides a richer set of commands than a typical key-value systems
    | such as APC or Memcached. Laravel makes it easy to dig right in.
    |
    */

    'redis' => [

        'client' => 'predis',

        'default' => [
            'host' => env('REDIS_HOST', '127.0.0.1'),
            'password' => env('REDIS_PASSWORD', null),
            'port' => env('REDIS_PORT', 6379),
            'database' => 0,
        ],

    ],

];

If I set the 'connection' => redis, it throws Database [redis] not configured. error. I'm using Redis as Cache, so a connection should already exists, or am I missing sth?