techdocsmith commented on a change in pull request #10848:
URL: https://github.com/apache/druid/pull/10848#discussion_r588580930
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File path: docs/querying/caching.md
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@@ -22,63 +22,75 @@ title: "Query caching"
~ under the License.
-->
+You can enable caching in Apache Druid to improve query times for frequently
accessed data. This topic defines the different types of caching for Druid. It
describes the default caching behavior and provides guidance and examples to
help you hone your caching strategy.
-Apache Druid supports query result caching at both the segment and whole-query
result level. Cache data can be stored in the
-local JVM heap or in an external distributed key/value store. In all cases,
the Druid cache is a query result cache.
-The only difference is whether the result is a _partial result_ for a
particular segment, or the result for an entire
-query. In both cases, the cache is invalidated as soon as any underlying data
changes; it will never return a stale
-result.
+If you're unfamiliar with Druid architecture, review the following topics
before proceeding with caching:
+- [Druid Design](../design/architecture.md)
+- [Segments](../design/segments.md)
+- [Query execution](./query-execution)
-Segment-level caching allows the cache to be leveraged even when some of the
underling segments are mutable and
-undergoing real-time ingestion. In this case, Druid will potentially cache
query results for immutable historical
-segments, while re-computing results for the real-time segments on each query.
Whole-query result level caching is not
-useful in this scenario, since it would be continuously invalidated.
+For instructions to configure caching see [Using query
caching](./using-caching.md).
-Segment-level caching does require Druid to merge the per-segment results on
each query, even when they are served
-from the cache. For this reason, whole-query result level caching can be more
efficient if invalidation due to real-time
-ingestion is not an issue.
+## Cache types
+Druid supports segment caching which stores _partial results_ of a query for a
specific segment, and whole-query caching which stores all results for a query.
To avoid returning stale results, Druid invalidates the cache the moment any
underlying data changes for both types of cache.
-## Using and populating cache
+Druid can store cache data the local JVM heap or in an external distributed
key/value store. See [Cache
configuration](../configuration/index.md#cache-configuration) for information
on how to configure cache storage.
Review comment:
I've added the (relevant?) defaults. These will need checking because
the language/code for the maximum cache storage was confusing.
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