himanshug opened a new pull request #8426: groupBy query: optional limit push down to segment scan URL: https://github.com/apache/incubator-druid/pull/8426 Fixes ##8413 ### Description This patch enables optimization to exploit limit push down in segment scan phase during V2 GroupBy query processing. At a high level following changes are introduced. - `applyLimitPushDownToSegment` property is introduced to enable this optimization both at cluster and query level (`true` by default) - `GroupByQueryEngineV2.HashAggregateIterator.newGrouper()` is updated to return `LimitedBufferHashGrouper` when `query.isApplyLimitPushDown() == true` - `GroupByQueryEngineV2.GroupByEngineKeySerde` is updated to correctly implement `Grouper.BufferComparator bufferComparator()` and `Grouper.BufferComparator bufferComparatorWithAggregators(..)` methods. - A new method `Grouper.BufferComparator bufferComparator(int keyBufferPosition, @Nullable StringComparator stringComparator)` is added to `GroupByColumnSelectorStrategy` - Code related to creation of Grouper.BufferComparator from `RowBasedGrouperHelper` into a new class `GrouperBufferComparatorUtils` for reuse. <hr> This PR has: - [X] been self-reviewed. - [X] added documentation for new or modified features or behaviors. - [X] been tested in a test Druid cluster. <hr>
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