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Improve caching doc (#7223) 

- Set correct default values for query context result cache parameters
- Add details about broker cache impact on local historical merging
This commit is contained in:
Pierre-Emile Ferron 2019-03-11 17:06:28 -07:00 committed by Gian Merlino
parent dcfca03718
commit a88fbcd5db
2 changed files with 4 additions and 4 deletions
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4
docs/content/querying/caching.md
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@ -35,8 +35,8 @@ can be enabled at either the Historical and Broker level (it is not recommended
## Query caching on Brokers
Enabling caching on the Broker can yield faster results than if query caches were enabled on Historicals for small clusters. This is
the recommended setup for smaller production clusters (< 20 servers). Take note that when caching is enabled on the Broker,
results from Historicals are returned on a per segment basis, and Historicals will not be able to do any local result merging.
the recommended setup for smaller production clusters (< 20 servers). Take note that when `druid.broker.cache.populateCache` is set to
`true`, results from Historicals are returned on a per segment basis, and Historicals will not be able to do any local result merging.
Result level caching is enabled only on the Broker side.
## Query caching on Historicals

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docs/content/querying/query-context.md
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@ -33,8 +33,8 @@ The query context is used for various query configuration parameters. The follow
|queryId | auto-generated | Unique identifier given to this query. If a query ID is set or known, this can be used to cancel the query |
|useCache | `true` | Flag indicating whether to leverage the query cache for this query. When set to false, it disables reading from the query cache for this query. When set to true, Druid uses druid.broker.cache.useCache or druid.historical.cache.useCache to determine whether or not to read from the query cache |
|populateCache | `true` | Flag indicating whether to save the results of the query to the query cache. Primarily used for debugging. When set to false, it disables saving the results of this query to the query cache. When set to true, Druid uses druid.broker.cache.populateCache or druid.historical.cache.populateCache to determine whether or not to save the results of this query to the query cache |
|useResultLevelCache | `false` | Flag indicating whether to leverage the result level cache for this query. When set to false, it disables reading from the query cache for this query. When set to true, Druid uses druid.broker.cache.useResultLevelCache to determine whether or not to read from the query cache |
|populateResultLevelCache | `false` | Flag indicating whether to save the results of the query to the result level cache. Primarily used for debugging. When set to false, it disables saving the results of this query to the query cache. When set to true, Druid uses druid.broker.cache.populateCache to determine whether or not to save the results of this query to the query cache |
|useResultLevelCache | `true` | Flag indicating whether to leverage the result level cache for this query. When set to false, it disables reading from the query cache for this query. When set to true, Druid uses druid.broker.cache.useResultLevelCache to determine whether or not to read from the query cache |
|populateResultLevelCache | `true` | Flag indicating whether to save the results of the query to the result level cache. Primarily used for debugging. When set to false, it disables saving the results of this query to the query cache. When set to true, Druid uses druid.broker.cache.populateCache to determine whether or not to save the results of this query to the query cache |
|bySegment | `false` | Return "by segment" results. Primarily used for debugging, setting it to `true` returns results associated with the data segment they came from |
|finalize | `true` | Flag indicating whether to "finalize" aggregation results. Primarily used for debugging. For instance, the `hyperUnique` aggregator will return the full HyperLogLog sketch instead of the estimated cardinality when this flag is set to `false` |
|chunkPeriod | `P0D` (off) | At the Broker process level, long interval queries (of any type) may be broken into shorter interval queries to parallelize merging more than normal. Broken up queries will use a larger share of cluster resources, but, if you use groupBy "v1, it may be able to complete faster as a result. Use ISO 8601 periods. For example, if this property is set to `P1M` (one month), then a query covering a year would be broken into 12 smaller queries. The broker uses its query processing executor service to initiate processing for query chunks, so make sure "druid.processing.numThreads" is configured appropriately on the broker. [groupBy queries](groupbyquery.html) do not support chunkPeriod by default, although they do if using the legacy "v1" engine. This context is deprecated since it's only useful for groupBy "v1", and will be removed in the future releases.|