--- layout: doc_page --- # Caching Caching can optionally be enabled on the broker, historical, and realtime processing. See [broker](broker.html#caching), [historical](historical.html#caching), and [realtime](realtime.html#caching) configuration options for how to enable it for different processes. Druid uses a local in-memory cache by default, unless a diffrent type of cache is specified. Use the `druid.cache.type` configuration to set a different kind of cache. ## Cache configuration Cache settings are set globally, so the same configuration can be re-used for both broker and historical nodes, when defined in the common properties file. |Property|Possible Values|Description|Default| |--------|---------------|-----------|-------| |`druid.cache.type`|`local`, `memcached`, `hybrid`, `caffeine`|The type of cache to use for queries. See below of the configuration options for each cache type|`caffeine`| #### Local Cache
DEPRECATED: Use caffeine (default as of v0.12.0) instead
The local cache is deprecated in favor of the Caffeine cache, and may be removed in a future version of Druid. The Caffeine cache affords significantly better performance and control over eviction behavior compared to `local` cache, and is recommended in any situation where you are using JRE 8u60 or higher. A simple in-memory LRU cache. Local cache resides in JVM heap memory, so if you enable it, make sure you increase heap size accordingly. |Property|Description|Default| |--------|-----------|-------| |`druid.cache.sizeInBytes`|Maximum cache size in bytes. Zero disables caching.|0| |`druid.cache.initialSize`|Initial size of the hashtable backing the cache.|500000| |`druid.cache.logEvictionCount`|If non-zero, log cache eviction every `logEvictionCount` items.|0| ### Caffeine Cache A highly performant local cache implementation for Druid based on [Caffeine](https://github.com/ben-manes/caffeine). Requires a JRE8u60 or higher if using `COMMON_FJP`. ##### Configuration Below are the configuration options known to this module: |`runtime.properties`|Description|Default| |--------------------|-----------|-------| |`druid.cache.type`| Set this to `caffeine` or leave out parameter|`caffeine`| |`druid.cache.sizeInBytes`|The maximum size of the cache in bytes on heap.|min(1GB, Runtime.maxMemory / 10)| |`druid.cache.expireAfter`|The time (in ms) after an access for which a cache entry may be expired|None (no time limit)| |`druid.cache.cacheExecutorFactory`|The executor factory to use for Caffeine maintenance. One of `COMMON_FJP`, `SINGLE_THREAD`, or `SAME_THREAD`|ForkJoinPool common pool (`COMMON_FJP`)| |`druid.cache.evictOnClose`|If a close of a namespace (ex: removing a segment from a node) should cause an eager eviction of associated cache values|`false`| ##### `druid.cache.cacheExecutorFactory` Here are the possible values for `druid.cache.cacheExecutorFactory`, which controls how maintenance tasks are run * `COMMON_FJP` (default) use the common ForkJoinPool. Should use with [JRE 8u60 or higher](https://github.com/druid-io/druid/pull/4810#issuecomment-329922810). Older versions of the JRE may have worse performance than newer JRE versions. * `SINGLE_THREAD` Use a single-threaded executor. * `SAME_THREAD` Cache maintenance is done eagerly. #### Metrics In addition to the normal cache metrics, the caffeine cache implementation also reports the following in both `total` and `delta` |Metric|Description|Normal value| |------|-----------|------------| |`query/cache/caffeine/*/requests`|Count of hits or misses|hit + miss| |`query/cache/caffeine/*/loadTime`|Length of time caffeine spends loading new values (unused feature)|0| |`query/cache/caffeine/*/evictionBytes`|Size in bytes that have been evicted from the cache|Varies, should tune cache `sizeInBytes` so that `sizeInBytes`/`evictionBytes` is approximately the rate of cache churn you desire| #### Memcached Uses memcached as cache backend. This allows all nodes to share the same cache. |Property|Description|Default| |--------|-----------|-------| |`druid.cache.expiration`|Memcached [expiration time](https://code.google.com/p/memcached/wiki/NewCommands#Standard_Protocol).|2592000 (30 days)| |`druid.cache.timeout`|Maximum time in milliseconds to wait for a response from Memcached.|500| |`druid.cache.hosts`|Comma separated list of Memcached hosts ``.|none| |`druid.cache.maxObjectSize`|Maximum object size in bytes for a Memcached object.|52428800 (50 MB)| |`druid.cache.memcachedPrefix`|Key prefix for all keys in Memcached.|druid| |`druid.cache.numConnections`|Number of memcached connections to use.|1| |`druid.cache.protocol`|Memcached communication protocol. Can be binary or text.|binary| |`druid.cache.locator`|Memcached locator. Can be consistent or array_mod.|consistent| #### Hybrid Uses a combination of any two caches as a two-level L1 / L2 cache. This may be used to combine a local in-memory cache with a remote memcached cache. Cache requests will first check L1 cache before checking L2. If there is an L1 miss and L2 hit, it will also populate L1. |Property|Description|Default| |--------|-----------|-------| |`druid.cache.l1.type`|type of cache to use for L1 cache. See `druid.cache.type` configuration for valid types.|`local`| |`druid.cache.l2.type`|type of cache to use for L2 cache. See `druid.cache.type` configuration for valid types.|`local`| |`druid.cache.l1.*`|Any property valid for the given type of L1 cache can be set using this prefix. For instance, if you are using a `local` L1 cache, specify `druid.cache.l1.sizeInBytes` to set its size.|defaults are the same as for the given cache type.| |`druid.cache.l2.*`|Prefix for L2 cache settings, see description for L1.|defaults are the same as for the given cache type.| |`druid.cache.useL2`|A boolean indicating whether to query L2 cache, if it's a miss in L1. It makes sense to configure this to `false` on historical nodes, if L2 is a remote cache like `memcached`, and this cache also used on brokers, because in this case if a query reached historical it means that a broker didn't find corresponding results in the same remote cache, so a query to the remote cache from historical is guaranteed to be a miss.|`true`| |`druid.cache.populateL2`|A boolean indicating whether to put results into L2 cache.|`true`|