mirror of https://github.com/apache/druid.git
40 lines
2.0 KiB
Markdown
40 lines
2.0 KiB
Markdown
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layout: doc_page
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---
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Druid Caffeine Cache
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--------------------
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A highly performant local cache implementation for Druid based on [Caffeine](https://github.com/ben-manes/caffeine). Requires a JRE8u60 or higher
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# Configuration
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Below are the configuration options known to this module:
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|`runtime.properties`|Description|Default|
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|--------------------|-----------|-------|
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|`druid.cache.sizeInBytes`|The maximum size of the cache in bytes on heap.|None (unlimited)|
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|`druid.cache.expireAfter`|The time (in ms) after an access for which a cache entry may be expired|None (no time limit)|
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|`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`)|
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|`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`|
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## `druid.cache.cacheExecutorFactory`
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Here are the possible values for `druid.cache.cacheExecutorFactory`, which controls how maintenance tasks are run
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* `COMMON_FJP` (default) use the common ForkJoinPool. Do NOT use this option unless you are running 8u60 or higher
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* `SINGLE_THREAD` Use a single-threaded executor
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* `SAME_THREAD` Cache maintenance is done eagerly
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# Enabling
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To enable the caffeine cache, include this module on the loadList and set `druid.cache.type` to `caffeine` in your properties.
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# Metrics
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In addition to the normal cache metrics, the caffeine cache implementation also reports the following in both `total` and `delta`
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|Metric|Description|Normal value|
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|------|-----------|------------|
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|`query/cache/caffeine/*/requests`|Count of hits or misses|hit + miss|
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|`query/cache/caffeine/*/loadTime`|Length of time caffeine spends loading new values (unused feature)|0|
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|`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|
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