druid/docs/development/extensions-contrib/redis-cache.md

id	title
redis-cache	Druid Redis Cache

To use this Apache Druid (incubating) extension, make sure to include druid-redis-cache extension.

A cache implementation for Druid based on Redis.

Below are the configuration options known to this module.

Note that just adding these properties does not enable the cache. You still need to add the druid.<process-type>.cache.useCache and druid.<process-type>.cache.populateCache properties for the processes you want to enable the cache on as described in the cache configuration docs.

A possible configuration would be to keep the properties below in your common.runtime.properties file (present on all processes) and then add druid.<nodetype>.cache.useCache and druid.<nodetype>.cache.populateCache in the runtime.properties file of the process types you want to enable caching on.

Configuration

common.runtime.properties	Description	Default	Required
druid.cache.host	Redis server host	None	yes
druid.cache.port	Redis server port	None	yes
druid.cache.expiration	Expiration(in milliseconds) for cache entries	24 * 3600 * 1000	no
druid.cache.timeout	Timeout(in milliseconds) for get cache entries from Redis	2000	no
druid.cache.maxTotalConnections	Max total connections to Redis	8	no
druid.cache.maxIdleConnections	Max idle connections to Redis	8	no
druid.cache.minIdleConnections	Min idle connections to Redis	0	no

Enabling

To enable the redis cache, include this module on the loadList and set druid.cache.type to redis in your properties.

Metrics

In addition to the normal cache metrics, the redis cache implementation also reports the following in both total and delta

Metric	Description	Normal value
query/cache/redis/*/requests	Count of requests to redis cache	whatever request to redis will increase request count by 1