mirror of https://github.com/apache/druid.git
3c493dc3ed
* Round-robin iterator for datasources to kill.
Currently there's a fairness problem in the KillUnusedSegments duty
where the duty consistently selects the same set of datasources as discovered
from the metadata store or dynamic config params. This is a problem especially
when there are multiple unused. In a medium to large cluster, while we can increase
the task slots to increase the likelihood of broader coverage. This patch adds a simple
round-robin iterator to select datasources and has the following properties:
1. Starts with an initial random cursor position in an ordered list of candidates.
2. Consecutive {@code next()} iterations from {@link #getIterator()} are guaranteed to be deterministic
unless the set of candidates change when {@link #updateCandidates(Set)} is called.
3. Guarantees that no duplicate candidates are returned in two consecutive {@code next()} iterations.
* Renames in RoundRobinIteratorTest.
* Address review comments.
1. Clarify javadocs on the ordered list. Also flesh out the details a bit more.
2. Rename the test hooks to make intent clearer and fix typo.
3. Add NotThreadSafe annotation.
4. Remove one potentially noisy log that's in the path of iteration.
* Add null check to input candidates.
* More commentary.
* Addres review feedback: downgrade some new info logs to debug; invert condition.
Remove redundant comments.
Remove rendundant variable tracking.
* CircularList adjustments.
* Updates to CircularList and cleanup RoundRobinInterator.
* One more case and add more tests.
* Make advanceCursor private for now.
* Review comments.
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