druid/docs/content/querying/query-context.md

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Query Context

The query context is used for various query configuration parameters. The following parameters apply to all queries.

property	default	description
timeout	druid.server.http.defaultQueryTimeout	Query timeout in millis, beyond which unfinished queries will be cancelled. 0 timeout means no timeout. To set the default timeout, see broker configuration
priority	0	Query Priority. Queries with higher priority get precedence for computational resources.
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
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 node 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 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 do not support chunkPeriod by default, although they do if using the legacy "v1" engine.
maxScatterGatherBytes	druid.server.http.maxScatterGatherBytes	Maximum number of bytes gathered from data nodes such as historicals and realtime processes to execute a query. This parameter can be used to further reduce maxScatterGatherBytes limit at query time. See broker configuration for more details.
maxQueuedBytes	druid.broker.http.maxQueuedBytes	Maximum number of bytes queued per query before exerting backpressure on the channel to the data server. Similar to maxScatterGatherBytes, except unlike that configuration, this one will trigger backpressure rather than query failure. Zero means disabled.
serializeDateTimeAsLong	false	If true, DateTime is serialized as long in the result returned by broker and the data transportation between broker and compute node
serializeDateTimeAsLongInner	false	If true, DateTime is serialized as long in the data transportation between broker and compute node

In addition, some query types offer context parameters specific to that query type.

TopN queries

property	default	description
minTopNThreshold	1000	The top minTopNThreshold local results from each segment are returned for merging to determine the global topN.

Timeseries queries

property	default	description
skipEmptyBuckets	false	Disable timeseries zero-filling behavior, so only buckets with results will be returned.

GroupBy queries

See GroupBy query context.