Redis (cache & sessions)

Since Maho 25.5 adds a completely new cache subsystem based on symfony/cache, Maho supports Redis for both cache and session storage out of the box, no 3rd party plugin needed.

Cache

If you want to enable it, and you've a Redis database available, simply head out to your local.xml file and configure the global/cache section this way:

<global>
    <cache>
        <lifetime>86400</lifetime> <!-- optional, default is 7200 -->
        <backend>redis</backend> <!-- optional, default is file -->
        <backend_options> <!-- optional for "file", required for "redis" -->
            <dsn>redis://localhost/0</dsn> <!-- TCP connection, database 0 -->
        </backend_options>
    </cache>
</global>

The dsn element supports many possible options, check out of the full documentation at Symfony's website. For example, using a Unix socket (often faster than TCP on the same host):

<dsn>redis:///var/run/redis/redis.sock/0</dsn>
<!-- Unix socket, database 0 -->

Sessions

Redis can also be used for session storage, independently from the cache:

<global>
    <session_save>redis</session_save>
    <redis_session>
        <dsn>redis:///var/run/redis/redis.sock/1</dsn> <!-- use a different database than the cache -->
        <key_prefix>maho_session:</key_prefix> <!-- optional -->
    </redis_session>
</global>

Sessions use the same DSN format as the cache (both TCP redis://host:port/db and Unix socket redis:///path/to/socket/db are supported). It's good practice to point sessions to a different database number than the cache.

Complete example with both cache and sessions

<global>
    <session_save>redis</session_save>
    <redis_session>
        <dsn>redis:///var/run/redis/redis.sock/1</dsn>
        <key_prefix>maho_session:</key_prefix>
    </redis_session>
    <cache>
        <lifetime>86400</lifetime>
        <backend>redis</backend>
        <backend_options>
            <dsn>redis:///var/run/redis/redis.sock/0</dsn>
        </backend_options>
    </cache>
</global>

Important: Redis maxmemory-policy requirement

Maho's cache backend uses Symfony's RedisTagAwareAdapter, which requires a maxmemory-policy of either noeviction or any volatile-* value (e.g. volatile-lfu, volatile-lru). The tag sets are stored without a TTL and must survive the cached items that have one, something the allkeys-* policies cannot guarantee.

Policies like allkeys-lfu or allkeys-lru cause the cache backend to silently fail to save any data, with no visible error.

Configure Redis accordingly in /etc/redis/redis.conf:

maxmemory-policy volatile-lfu

volatile-lfu provides the same LFU eviction behavior as allkeys-lfu, but only evicts keys that have a TTL set (cache data), preserving tag metadata keys that have no expiration. This requirement applies even when maxmemory is 0 (unlimited), because the adapter checks the reported policy regardless of whether eviction would actually happen. On managed Redis (AWS ElastiCache, Redis Cloud, etc.) change it from the provider's parameter group / dashboard.

You can also apply the change at runtime (set it in redis.conf too, or it's lost on restart):

redis-cli CONFIG SET maxmemory-policy volatile-lfu