Shopware uses Symfony's Lock component to implement locking functionality. By default, Symfony will use a local lock store, this means in multi-machine (cluster) setups naive file locks will break the system, therefore it is highly recommended using one of the supported remote stores.
Using Redis as a lock store
As Redis can already be used for caching, increment store and session storage, you can also use that Redis host as a remote lock store. To use Redis, create a config/packages/framework.yml file with the following content
Other lock stores
As Shopware uses Symfony's Lock component all lock stores supported by Symfony can be used. Keep in mind that you should always use a remote store if you host shopware in a cluster setup. For a list of all available lock stores refer to Symfony's documentation. There are also more detailed information on the configuration options.