mirror of https://github.com/apache/druid.git
47 lines
2.4 KiB
Markdown
47 lines
2.4 KiB
Markdown
---
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layout: doc_page
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title: "Query Caching"
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---
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# Query Caching
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Druid supports query result caching through an LRU cache. Results are stored as a whole or either on a per segment basis along with the
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parameters of a given query. Segment level caching allows Druid to return final results based partially on segment results in the cache
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and partially on segment results from scanning historical/real-time segments. Result level caching enables Druid to cache the entire
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result set, so that query results can be completely retrieved from the cache for identical queries.
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Segment results can be stored in a local heap cache or in an external distributed key/value store. Segment query caches
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can be enabled at either the Historical and Broker level (it is not recommended to enable caching on both).
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## Query caching on Brokers
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Enabling caching on the Broker can yield faster results than if query caches were enabled on Historicals for small clusters. This is
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the recommended setup for smaller production clusters (< 20 servers). Take note that when caching is enabled on the Broker,
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results from Historicals are returned on a per segment basis, and Historicals will not be able to do any local result merging.
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Result level caching is enabled only on the Broker side.
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## Query caching on Historicals
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Larger production clusters should enable caching only on the Historicals to avoid having to use Brokers to merge all query
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results. Enabling caching on the Historicals instead of the Brokers enables the Historicals to do their own local result
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merging and puts less strain on the Brokers.
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