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Posted to commits@druid.apache.org by "nozjkoitop (via GitHub)" <gi...@apache.org> on 2025/12/19 08:12:53 UTC
[PR] Feature fix msq with hllsketch in realtime (druid)
nozjkoitop opened a new pull request, #18859:
URL: https://github.com/apache/druid/pull/18859
This PR is a refreshed version of the previously closed PR: https://github.com/apache/druid/pull/16607
It fixes a failure when MSQ queries run with "includeSegmentSource": "REALTIME" while a supervisor is ingesting and the query reads realtime data.
Before Druid 31, the UI surfaced a ClassCastException (stack trace below). In newer versions it appears as an NPE, but the underlying cause is the same
````
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
````
On the realtime segment path, the selector’s getObject() (used by ComplexFieldWriter) can return a byte[] that is already the serialized form of an HLL sketch.
However, later serde assumes the complex metric value is the object form (HllSketchHolder) and passes it into HllSketchHolderObjectStrategy.toBytes(), which expects an HllSketchHolder. When it receives a byte[] instead, it results in the ClassCastException shown above.
## How to reproduce
Run an MSQ select for a realtime data with "includeSegmentSource": "REALTIME" in the context
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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Re: [PR] Fixed ClassCastException during Multi-Stage Queries on real-time segments (druid)
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] closed pull request #18859: Fixed ClassCastException during Multi-Stage Queries on real-time segments
URL: https://github.com/apache/druid/pull/18859
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Re: [PR] Fixed ClassCastException during Multi-Stage Queries on real-time segments (druid)
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #18859:
URL: https://github.com/apache/druid/pull/18859#issuecomment-4274871670
This pull request/issue has been closed due to lack of activity. If you think that
is incorrect, or the pull request requires review, you can revive the PR at any time.
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Re: [PR] Fixed ClassCastException during Multi-Stage Queries on real-time segments (druid)
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #18859:
URL: https://github.com/apache/druid/pull/18859#issuecomment-4105020094
This pull request has been marked as stale due to 60 days of inactivity.
It will be closed in 4 weeks if no further activity occurs. If you think
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Re: [PR] Fixed ClassCastException during Multi-Stage Queries on real-time segments (druid)
Posted by "nozjkoitop (via GitHub)" <gi...@apache.org>.
nozjkoitop commented on PR #18859:
URL: https://github.com/apache/druid/pull/18859#issuecomment-3674741602
Hey @LakshSingla @adarshsanjeev can you help in reviewing this? As you already participated in my previous attempt to fix that :)
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