Caching in applications #

This page is for application creators who cache computed data and rendered output. Caching makes pages fast; a wrong key or a missing clear shows one user another user's data or keeps stale data forever.

Contents #

1. The kernel's caches
2. Template output: cache blocks
3. Computed data in PHP
4. Clearing
5. Under persistent workers

The kernel's caches #

The full list with ids and tags: 10.6 Caches.

Template output: cache blocks #

{cache-block keys=array( 'expdemo-stats', $current_user.contentobject_id ) expiry=300}
  {def $stats = fetch( 'expdemo', 'stats', hash() )} ... {undef $stats}
{/cache-block}

Data from your own tables does not trigger the publish clear: choose an expiry that matches how stale it may be, or add ignore_content_expiry and clear the template-block cache yourself when your data changes (Template functions, includes and cache blocks).

Computed data in PHP #

Store expensive results through the kernel's cluster file handler, so they work on one server and on a cluster:

$file = eZClusterFileHandler::instance( eZSys::cacheDirectory() . '/expdemo/stats.cache' );
$stats = $file->processCache(
    function ( $path, $mtime ) {                                          // read a valid cache file
        return json_decode( (string)file_get_contents( $path ), true );
    },
    function ( $path ) {                                                  // generate when expired or missing
        $stats = expDemoStats::compute();
        return array( 'content' => $stats, 'binarydata' => json_encode( $stats ), 'scope' => 'expdemo-stats' );
    },
    300 );                                                                // $ttl: seconds from storing

processCache( $retrieveCallback, $generateCallback = null, $ttl = null, $expiry = null, $extraData = null ) is documented in kernel/classes/clusterfilehandlers/ezfsfilehandler.php: the retrieve callback gets the path and the mtime, the generate callback the path and returns content (returned to you) and binarydata (written to the file); while one process generates, others wait instead of generating the same data.

Clearing #

• Clear what you cached when its source changes: in the code that changes it, or in a workflow event or listener.
• Give your cache a directory of its own so it can be removed alone.
• An extension can add its cache to the cache list (site.ini [Cache] CacheItems[] and a [Cache_<id>] block, as the shipped [Cache_rest] does), so ezcache.php --clear-id=<id> and Setup > Caches can clear it, as the kernel's [Cache_*] blocks do.

Under persistent workers #

Velocity keeps PHP processes between requests: a static variable or a singleton survives into the next request. Never keep user-specific data in static variables; reset per-request state, or key it by request. Process memory is not shared between workers, so it is not a shared cache either (Velocity persistent worker server).

Related pages #

• View cache and cache blocks
• Caches
• Caching cookbook (doc/eng-us/examples/cookbook/caching.md)
• Free documentation: this page is free to copy, translate and improve under the GNU FDL 1.3.