L2 cache configuration

Caching enables a reduction in network traffic between the remote cache storage and the Commerce application. A standard Commerce instance transfers around 300 kb per request, and traffic may quickly grow to over ~1000 requests in some situations.

To reduce the network bandwidth to Redis, store cache data locally on each web node and use the remote cache for two purposes:

  • Check the cache data version and ensure that the latest cache is stored locally
  • Transfer the latest cache from the remote machine to the local machine

Commerce stores the hashed data version in Redis, with the suffix ‘:hash’ appended to the regular key. If there is an outdated local cache, the data is transferred to the local machine with a cache adapter.

INFO

For Adobe Commerce on cloud infrastructure, consider the best practices in the Extended Redis cache implementation support article.

Configuration example

Use the following example to modify or replace the existing cache section in the app/etc/env.php file.

'cache' => [
    'frontend' => [
        'default' => [
            'backend' => '\\Magento\\Framework\\Cache\\Backend\\RemoteSynchronizedCache',
            'backend_options' => [
                'remote_backend' => '\\Magento\\Framework\\Cache\\Backend\\Redis',
                'remote_backend_options' => [
                    'persistent' => 0,
                    'server' => 'localhost',
                    'database' => '0',
                    'port' => '6379',
                    'password' => '',
                    'compress_data' => '1',
                ],
                'local_backend' => 'Cm_Cache_Backend_File',
                'local_backend_options' => [
                    'cache_dir' => '/dev/shm/'
                ],
                'use_stale_cache' => false,
            ],
            'frontend_options' => [
                'write_control' => false,
            ],
        ]
    ],
    'type' => [
        'default' => ['frontend' => 'default'],
    ],
],

Where:

  • backend is the L2 cache implementation.
  • backend_options is the L2 cache configuration.
    • remote_backend is the remote cache implementation: Redis or MySQL.
    • remote_backend_options is the remote cache configuration.
    • local_backend is the local cache implementation: Cm_Cache_Backend_File
    • local_backend_options is the local cache configuration.
      • cache_dir is a file cache-specific option for the directory where the local cache is stored.
    • use_stale_cache is a flag that enables or disables the use of stale cache.

Adobe recommends using Redis for remote caching (\Magento\Framework\Cache\Backend\Redis) and Cm_Cache_Backend_File for the local caching of data in shared memory, using: 'local_backend_options' => ['cache_dir' => '/dev/shm/']

Adobe recommends the use of the cache preload feature, as it drastically decreases the pressure on Redis. Do not forget to add the suffix ‘:hash’ for preload keys.

Stale cache options

Starting with Commerce 2.4, the stale_cache option can improve performance in some specific cases.

Generally, the trade-off with lock waiting is acceptable from the performance side, but the larger the number of Blocks or Cache the merchant has, the more time is spent waiting for locks. In some scenarios, you can wait a numbers of keys * lookup timeout amount of time for the process. In some rare cases, the merchant can have hundreds of keys in the Block/Config cache, so even small lookup timeout for lock may cost seconds.

Stale cache only works with a L2 cache. With a stale cache, you could send an outdated cache, while a new one is generating in a parallel process. To enable stale cache, add 'use_stale_cache' => true to top config of the L2 cache.

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