kfaraz opened a new pull request, #18274:
URL: https://github.com/apache/druid/pull/18274
### Description
Historical cloning can sometimes cause segment downloads to fail due to the
load spec being null.
Example:
```
org.apache.druid.segment.loading.SegmentLoadingException: Exception loading
segment[xyz]
at
org.apache.druid.server.coordination.SegmentLoadDropHandler.addSegment(SegmentLoadDropHandler.java:177)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.server.coordination.SegmentLoadDropHandler$1.lambda$addSegment$1(SegmentLoadDropHandler.java:333)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:539)
[?:?]
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
[?:?]
at
java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
[?:?]
at
java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
[?:?]
at java.base/java.lang.Thread.run(Thread.java:840) [?:?]
Caused by: java.lang.NullPointerException: Cannot invoke
"org.apache.druid.segment.loading.LoadSpec.loadSegment(java.io.File)" because
"loadSpec" is null
at
org.apache.druid.segment.loading.SegmentLocalCacheManager$SegmentCacheEntry.loadInLocation(SegmentLocalCacheManager.java:844)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.segment.loading.SegmentLocalCacheManager$SegmentCacheEntry.loadInLocationWithStartMarker(SegmentLocalCacheManager.java:824)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.segment.loading.SegmentLocalCacheManager$SegmentCacheEntry.mount(SegmentLocalCacheManager.java:751)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.segment.loading.SegmentLocalCacheManager.assignLocationAndMount(SegmentLocalCacheManager.java:593)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.segment.loading.SegmentLocalCacheManager.load(SegmentLocalCacheManager.java:357)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
io.imply.druid.query.lookup.DelegatingSegmentCacheManagerWithCallbacks.load(DelegatingSegmentCacheManagerWithCallbacks.java:72)
~[?:?]
at
org.apache.druid.server.SegmentManager.loadSegment(SegmentManager.java:268)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
at
org.apache.druid.server.coordination.SegmentLoadDropHandler.addSegment(SegmentLoadDropHandler.java:173)
~[druid-server-2025.10.0-iap.jar:2025.10.0-iap]
... 6 more
```
I have not been able to reproduce this issue.
Tried several things with the embedded test in this PR.
The fix however would be to ensure that we send a loadable `DataSegment` to
the clone,
one with the `loadSpec` populated correctly.
`TierSegmentBalancer.getLoadableSegment` already does something similar.
### Changes
- Fix `CloneHistoricals` to send a loadable segment to the clones for loading
- Add `HistoricalCloningTest` which uses embedded cluster
<hr>
This PR has:
- [ ] been self-reviewed.
- [ ] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
(Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] 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)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [ ] 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.
- [ ] been tested in a test Druid cluster.
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