nozjkoitop opened a new pull request, #16607:
URL: https://github.com/apache/druid/pull/16607
Fixed issue when msq queries throw ClassCastException with
`"includeSegmentSource": "REALTIME"` and supervisor running.
````
Caused by: java.lang.ClassCastException: class [B cannot be cast to class
org.apache.druid.query.aggregation.datasketches.hll.HllSketchHolder ([B is in
module java.base of loader 'bootstrap';
org.apache.druid.query.aggregation.datasketches.hll.HllSketchHolder is in
unnamed module of loader java.net.URLClassLoader @38792286)
at
org.apache.druid.query.aggregation.datasketches.hll.HllSketchHolderObjectStrategy.toBytes(HllSketchHolderObjectStrategy.java:31)
at
org.apache.druid.segment.serde.ComplexMetricSerde.toBytes(ComplexMetricSerde.java:119)
at
org.apache.druid.frame.field.ComplexFieldWriter.writeTo(ComplexFieldWriter.java:65)
at
org.apache.druid.frame.write.RowBasedFrameWriter.writeDataUsingFieldWriters(RowBasedFrameWriter.java:291)
at
org.apache.druid.frame.write.RowBasedFrameWriter.writeData(RowBasedFrameWriter.java:246)
at
org.apache.druid.frame.write.RowBasedFrameWriter.addSelection(RowBasedFrameWriter.java:122)
at
org.apache.druid.msq.querykit.scan.ScanQueryFrameProcessor.populateFrameWriterAndFlushIfNeeded(ScanQueryFrameProcessor.java:348)
at
org.apache.druid.msq.querykit.scan.ScanQueryFrameProcessor.populateFrameWriterAndFlushIfNeededWithExceptionHandling(ScanQueryFrameProcessor.java:329)
at
org.apache.druid.msq.querykit.scan.ScanQueryFrameProcessor.runWithLoadedSegment(ScanQueryFrameProcessor.java:231)
at
org.apache.druid.msq.querykit.BaseLeafFrameProcessor.runIncrementally(BaseLeafFrameProcessor.java:87)
at
org.apache.druid.msq.querykit.scan.ScanQueryFrameProcessor.runIncrementally(ScanQueryFrameProcessor.java:158)
at
org.apache.druid.frame.processor.FrameProcessors$1FrameProcessorWithBaggage.runIncrementally(FrameProcessors.java:75)
at
org.apache.druid.frame.processor.FrameProcessorExecutor$1ExecutorRunnable.runProcessorNow(FrameProcessorExecutor.java:230)
... 8 more
````
After some investigation was found that selector's
[getObject()](https://github.com/apache/druid/blob/eb842d3ddadb21718c1e9703976c305b60406623/processing/src/main/java/org/apache/druid/frame/field/ComplexFieldWriter.java#L54)
for real-time segments was returning a byte array representation of HllSketch
but still was trying to convert it to a byte[]. While
HllSketchHolderObjectStrategy expects to have HllSketchHolder instance in
[toBytes()](https://github.com/apache/druid/blob/eb842d3ddadb21718c1e9703976c305b60406623/extensions-core/datasketches/src/main/java/org/apache/druid/query/aggregation/datasketches/hll/HllSketchHolderObjectStrategy.java#L59)
leading to the ClassCastException.
This PR has:
- [x] been self-reviewed.
- [ ] added documentation for new or modified features or behaviors.
- [ ] a release note entry in the PR description.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [x] been tested in a test Druid cluster.
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