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Caching
Caching can optionally be enabled on the broker and / or historical nodes. See the broker and historical configuration options for how to enable it for individual node types.
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 |
The type of cache to use for queries. See below of the configuration options for each cache type | local |
Local Cache
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 |
Memcached
Uses memcached as cache backend. This allows all nodes to share the same cache.
| Property | Description | Default |
|---|---|---|
druid.cache.expiration |
Memcached expiration time. | 2592000 (30 days) |
druid.cache.timeout |
Maximum time in milliseconds to wait for a response from Memcached. | 500 |
druid.cache.hosts |
Command separated list of Memcached hosts <host:port>. |
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 |
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. |