Using Memcache

Requirements¶

• A running memcached server and the address it listens on
• The PHP memcached extension on the server running MODX

::: warning The extension is named memcached, not memcache. The latter was removed in PHP 7 and MODX 3.x requires PHP 8.1 or newer, so no supported installation has it. :::

Setting up Memcache in MODX¶

Go to System Settings and set cache_handler to xPDO\Cache\xPDOMemCached.

The value is the full namespaced class name. The dot-separated form cache.xPDOMemCache from MODX 2.x no longer resolves: the class cannot be loaded, the log records Could not load class: cache.xPDOMemCache, and the site keeps writing to files.

To point MODX at the memcached server, create the default_memcached_server system setting with a value like localhost:11211. Several servers are listed separated by commas: server1.tld:11211,server2.tld:11211.

Every partition reads its own counterpart setting, named after it — resource_memcached_server, scripts_memcached_server. A single memcached_server setting works as a shared default.

Why the setting may appear to have no effect¶

MODX builds the cache manager before it reads system settings from the database, because it needs a handler to read them. A cache_handler stored as a system setting therefore arrives too late: on the next request MODX still builds the file-based handler, and writes the settings cache to disk through it.

To take effect immediately, set the handler in core/config/config.inc.php instead:

$config_options = [
    'cache_handler' => 'xPDO\\Cache\\xPDOMemCached',
    'default_memcached_server' => 'localhost:11211',
];

Empty core/cache/ afterwards, so the settings cache is rebuilt through the new handler.

Sharing one server between several sites¶

If you run more than one MODX site against the same memcached instance, give each site its own cache_prefix, for example site_a_. Without it the sites overwrite each other's entries.

See Also¶

• Caching — core partitions and the settings that pick their handler