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Fix groupBy docs to reflect that 'v2' is default. (#3993)

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Gian Merlino 2017-03-02 15:13:39 -08:00 committed by Jonathan Wei
parent 81a5f9851f
commit 3e8dbd59f8
1 changed files with 27 additions and 27 deletions
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docs/content/querying/groupbyquery.md
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@ -121,7 +121,14 @@ GroupBy queries can be executed using two different strategies. The default stra
"druid.query.groupBy.defaultStrategy" runtime property on the broker. This can be overridden using "groupByStrategy" in
the query context. If neither the context field nor the property is set, the "v2" strategy will be used.
- "v1", the default, generates per-segment results on data nodes (historical, realtime, middleManager) using a map which
- "v2", the default, is designed to offer better performance and memory management. This strategy generates
per-segment results using a fully off-heap map. Data nodes merge the per-segment results using a fully off-heap
concurrent facts map combined with an on-heap string dictionary. This may optionally involve spilling to disk. Data
nodes return sorted results to the broker, which merges result streams using an N-way merge. The broker materializes
the results if necessary (e.g. if the query sorts on columns other than its dimensions). Otherwise, it streams results
back as they are merged.
- "v1", a legacy engine, generates per-segment results on data nodes (historical, realtime, middleManager) using a map which
is partially on-heap (dimension keys and the map itself) and partially off-heap (the aggregated values). Data nodes then
merge the per-segment results using Druid's indexing mechanism. This merging is multi-threaded by default, but can
optionally be single-threaded. The broker merges the final result set using Druid's indexing mechanism again. The broker
@ -129,13 +136,6 @@ merging is always single-threaded. Because the broker merges results using the i
the full result set before returning any results. On both the data nodes and the broker, the merging index is fully
on-heap by default, but it can optionally store aggregated values off-heap.
- "v2" (experimental) is designed to offer better performance and memory management. This strategy generates
per-segment results using a fully off-heap map. Data nodes merge the per-segment results using a fully off-heap
concurrent facts map combined with an on-heap string dictionary. This may optionally involve spilling to disk. Data
nodes return sorted results to the broker, which merges result streams using an N-way merge. The broker materializes
the results if necessary (e.g. if the query sorts on columns other than its dimensions). Otherwise, it streams results
back as they are merged.
#### Alternatives
There are some situations where other query types may be a better choice than groupBy.
@ -158,15 +158,6 @@ strategy perform the outer query on the broker in a single-threaded fashion.
#### Server configuration
When using the "v1" strategy, the following runtime properties apply:
|Property|Description|Default|
|--------|-----------|-------|
|`druid.query.groupBy.defaultStrategy`|Default groupBy query strategy.|v2|
|`druid.query.groupBy.maxIntermediateRows`|Maximum number of intermediate rows for the per-segment grouping engine. This is a tuning parameter that does not impose a hard limit; rather, it potentially shifts merging work from the per-segment engine to the overall merging index. Queries that exceed this limit will not fail.|50000|
|`druid.query.groupBy.maxResults`|Maximum number of results. Queries that exceed this limit will fail.|500000|
|`druid.query.groupBy.singleThreaded`|Merge results using a single thread.|false|
When using the "v2" strategy, the following runtime properties apply:
|Property|Description|Default|
@ -182,18 +173,17 @@ This may require allocating more direct memory. The amount of direct memory need
ensure at least this amount of direct memory is available by providing `-XX:MaxDirectMemorySize=<VALUE>` at the command
line.
When using the "v1" strategy, the following runtime properties apply:
|Property|Description|Default|
|--------|-----------|-------|
|`druid.query.groupBy.defaultStrategy`|Default groupBy query strategy.|v2|
|`druid.query.groupBy.maxIntermediateRows`|Maximum number of intermediate rows for the per-segment grouping engine. This is a tuning parameter that does not impose a hard limit; rather, it potentially shifts merging work from the per-segment engine to the overall merging index. Queries that exceed this limit will not fail.|50000|
|`druid.query.groupBy.maxResults`|Maximum number of results. Queries that exceed this limit will fail.|500000|
|`druid.query.groupBy.singleThreaded`|Merge results using a single thread.|false|
#### Query context
When using the "v1" strategy, the following query context parameters apply:
|Property|Description|
|--------|-----------|
|`groupByStrategy`|Overrides the value of `druid.query.groupBy.defaultStrategy` for this query.|
|`groupByIsSingleThreaded`|Overrides the value of `druid.query.groupBy.singleThreaded` for this query.|
|`maxIntermediateRows`|Can be used to lower the value of `druid.query.groupBy.maxIntermediateRows` for this query.|
|`maxResults`|Can be used to lower the value of `druid.query.groupBy.maxResults` for this query.|
|`useOffheap`|Set to true to store aggregations off-heap when merging results.|
When using the "v2" strategy, the following query context parameters apply:
|Property|Description|
@ -204,3 +194,13 @@ When using the "v2" strategy, the following query context parameters apply:
|`maxMergingDictionarySize`|Can be used to lower the value of `druid.query.groupBy.maxMergingDictionarySize` for this query.|
|`maxOnDiskStorage`|Can be used to lower the value of `druid.query.groupBy.maxOnDiskStorage` for this query.|
|`sortByDimsFirst`|Sort the results first by dimension values and then by timestamp.|
When using the "v1" strategy, the following query context parameters apply:
|Property|Description|
|--------|-----------|
|`groupByStrategy`|Overrides the value of `druid.query.groupBy.defaultStrategy` for this query.|
|`groupByIsSingleThreaded`|Overrides the value of `druid.query.groupBy.singleThreaded` for this query.|
|`maxIntermediateRows`|Can be used to lower the value of `druid.query.groupBy.maxIntermediateRows` for this query.|
|`maxResults`|Can be used to lower the value of `druid.query.groupBy.maxResults` for this query.|
|`useOffheap`|Set to true to store aggregations off-heap when merging results.|