Druid Redis Cache

A cache implementation for Druid based on Redis.

Below are guidance and configuration options known to this module.

Installation

Use pull-deps tool shipped with Druid to install this extension on broker, historical and middle manager nodes.

java -classpath "druid_dir/lib/*" org.apache.druid.cli.Main tools pull-deps -c org.apache.druid.extensions.contrib:druid-redis-cache:{VERSION}

Enabling

To enable this extension after installation,

1. include this druid-redis-cache extension
2. to enable cache on broker nodes, follow broker caching docs to set related properties
3. to enable cache on historical nodes, follow historical caching docs to set related properties
4. to enable cache on middle manager nodes, follow peon caching docs to set related properties
5. set druid.cache.type to redis
6. add the following properties

Configuration

Cluster mode

To utilize a redis cluster, following properties must be set.

Note: some redis cloud service providers provide redis cluster service via a redis proxy, for these clusters, please follow the Standalone mode configuration below.

Properties	Description	Default	Required
druid.cache.cluster.nodes	Redis nodes in a cluster, represented in comma separated string. See example below	None	yes
druid.cache.cluster.maxRedirection	Max retry count	5	no

Example

# a typical redis cluster with 6 nodes
druid.cache.cluster.nodes=127.0.0.1:7001,127.0.0.1:7002,127.0.0.1:7003,127.0.0.1:7004,127.0.0.1:7005,127.0.0.1:7006

Standalone mode

To use a standalone redis, following properties must be set.

Properties	Description	Default	Required
druid.cache.host	Redis server host	None	yes
druid.cache.port	Redis server port	None	yes
druid.cache.database	Redis database index	0	no

Note: if both druid.cache.cluster.nodes and druid.cache.host are provided, cluster mode is preferred.

Shared Properties

Except for the properties above, there are some extra properties which can be customized to meet different needs.

Properties	Description	Default	Required
druid.cache.password	Password to access redis server/cluster	None	no
druid.cache.expiration	Expiration for cache entries	P1D	no
druid.cache.timeout	Timeout for connecting to Redis and reading entries from Redis	PT2S	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

For druid.cache.expiration and druid.cache.timeout properties, values can be format of Period or a number in milliseconds.

# Period format(recomended)
# cache expires after 1 hour
druid.cache.expiration=PT1H

# or in number(milliseconds) format
# 1 hour = 3_600_000 milliseconds
druid.cache.expiration=3600000

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