config.yml

doctrine:
    orm:
        auto_mapping: true
        metadata_cache_driver: apc
        query_cache_driver:
            type: service
            id: my_doctrine_common_cache_service
        result_cache_driver:
            type: memcache
            host: localhost
            port: 11211
            instance_class: Memcache

http://symfony.com/doc/current/reference/configuration/doctrine.html