Virushade

Aggregate functions on string columns

1

Fixes #16956. ### Description This PR introduces min() and max() aggregators for string columns: `StringMinAggregator` and `StringMaxAggregator`, and their respective buffer and vector aggregators. These aggregators compute the minimum and...

### Description Currently, Kubernetes jobs will retry for a total of 10 times to create a peon pod for ingestion tasks. However, there are some pain points that surface during...

Exact Cardinality Count extension

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### Description This PR introduces the `druid-exact-count` extension, providing a new aggregation function for computing the exact distinct count of values within a dimension. Unlike approximate estimators like HyperLogLog, this...

### Description According to the [log4j2 javadocs](https://logging.apache.org/log4j/2.x/javadoc/log4j-core/org/apache/logging/log4j/core/config/AppenderRef.html), `Appender-ref` is an alias for `AppenderRef`. I think we should standardize to use `AppenderRef` in our examples, so as not to confuse the...

Concurrent loading segment cache

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### Description #### Concurrent loading of cached segments during startup Previously, we are using 1 thread to run `SegmentLocalCacheManager#getCachedSegments`. We may take quite a bit of time if the number...

Attempt at #18781 . ### Description #### Metrics Reporting via GroupByQueryMetrics - Remove method signatures in codebase which rely on using PerQueryStats to retrieve metrics, and retrieve query stats via...

[Groupby Query Metrics] Add merge buffer tracking

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Fixes #17902 Huge thanks to @gianm for the implementation tip in the issue! ### Description #### Tracking merge buffer usage - Usage of a direct byte buffer is done under...

Possibly fixes #17944 ### Motivation Currently, we have GroupByStatsMonitor, which provide metrics for GroupBy queries by: Aggregating results of all GroupBy metrics in a certain time interval. Emit them regularly...

Historical Startup -- Configurable loading strategy

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Fixes #18446 ### Description This PR belongs to a set of PR's that hope to optimize the start-up time of Historical. I came across this problem when I am running...

Historical Segment Cache Loading Strategy on Start-up

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### Description - Propose a configurable startup strategy that eagerly loads only recent (“hot”) segments, while leaving older (“cold”) segments to load lazily on first access. - Propose to deprecate...