Shopware, by default, uses the session storage configured in PHP. On most installations, this is the file system. In smaller setups, you will not need to take care of sessions. However, for larger setups using clustering or with a lot of traffic, you will probably configure alternative session storage, such as Redis, to reduce the load on the database.

Session adapters

Configure Redis using PHP.ini

By default, Shopware uses the settings configured in PHP. You can reconfigure the Session config directly in your php.ini. Here is an example of configuring it directly in PHP.
session.save_handler = redis
session.save_path = "tcp://host:6379"
Please refer to the official PhpRedis documentation for all possible options.

Configure Redis using Shopware configuration

If you don't have access to the php.ini configuration, you can configure it directly in Shopware itself. For this, create a config/packages/redis.yml file with the following content:
# config/packages/redis.yml
handler_id: "redis://host:port"

Other adapters

Symfony also provides PHP implementations of some adapters:
To use one of these handlers, you must create a new service in the dependency injection and set the handler_id to the service id.
Example service definition:
<service id="session.db" class="Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler">
<argument ....></argument>
Example session configuration:
# config/packages/redis.yml
handler_id: "session.db"