# Caching System

Pootle uses a caching system to improve performance. It is an essential part of optimizing your Pootle installation. It is based on Django’s caching system, and is used for various things:

- To serve cached (possibly slightly outdated) versions of most pages to anonymous users to reduce their impact on server performance.
- To cache bits of the user interface, even for logged in users. Data will not be out of date but Pootle still tries to use the cache to reduce the impact on server performance.
- To store the result of expensive calculations like translation statistics.
- To keep track of last update timestamps to avoid unnecessary and expensive file operations (for example don’t attempt to save translations before a download if there are no new translations).

Without a well functioning cache system, Pootle could be slow.

## Cache Backends

Django supports multiple cache backends (methods of storing cache data). You can specify which backend to use by overriding the value of `CACHES` in your configuration file.

### Memcached

    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
            'LOCATION': '127.0.0.1:11211',
        }
    }

Memcached is the recommended cache backend, it provides the best performance. And works fine with multiprocessing servers like Apache. It requires the python-memcached package and a running memcached server. Due to extra dependencies it is not enabled by default.

#### Memcached on Unix sockets

    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
            'LOCATION': 'unix:/path/to/memcached.sock',
        }
    }

If you don’t want Pootle using TCP/IP to access memcached then you can use Unix sockets. This is often a situation in hardened installations using SELinux.

You will need to ensure that memcached is running with the `-s` option:

    $ memcached -u nobody -s /path/to/memcached.sock -a 0777

### Database

    CACHES = {
        'default': {
            'BACKEND': 'django.core.cache.backends.db.DatabaseCache',
            'LOCATION': 'my_cache_table',
        }
    }

Database caching relies on a table in the main Pootle database for storing the cached data, which makes it suitable for multiprocessing servers, with the added benefit that the cached data remains intact after a server reboot (unlike memcached) but it is considerably slower than memcached.

Changed in version 2.1.1.

This is the default cache backend. On new installs and upgrades the required database will be created.

Users of older versions need to create the cache tables manually if they would like to switch to the database cache backend using this management command:

    $ pootle createcachetable pootlecache