Prerequisite Install Redis service (daemon) on your Moodle server (see https://docs.moodle.org/37/en/Redis_cache_store#Installing_Redis_server ) if you do not already have it. Install the PHP extension Redis (see https://docs.moodle.org/37/en/Redis_cache_store#Installing_Redis_php_driver ) if you do not already have it. Start the Redis daemon (eg. redis-server /usr/local/etc/redis.conf ). Test 1 Visit 'Site administration' > 'Plugins' > 'Caching' > 'Configuration'. Click 'Add instance' next to 'Redis'. Confirm the options next to Use compressor are 'No compression' and 'Use gzip compression' Test 2 Install the PHP extension zstd see https://github.com/kjdev/php-ext-zstd for information on ways to install this by reading the README. Visit 'Site administration' > 'Plugins' > 'Caching' > 'Configuration'. Click 'Add instance' next to 'Redis'. Confirm the options next to Use compressor are 'No compression', 'Use gzip compression' AND 'Zstandard compression'. Set the 'Store name' and the 'Server' to the address your Redis server is running on (in my case 127.0.0.1) and save. Visit 'Language string cache' and next to it click 'Edit mappings' Set the 'Primary store' to the store you created earlier. Purge the caches. Confirm browsing still works. Test 3. Add the following to your config.php file define('TEST_CACHESTORE_REDIS_TESTSERVERS', '127.0.0.1'); Run the unit tests vendor/bin/phpunit cache/stores/redis/tests/compressor_test.php .