Fly-Style commented on code in PR #19034:
URL: https://github.com/apache/druid/pull/19034#discussion_r2827049799
##########
indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/supervisor/SeekableStreamSupervisor.java:
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@@ -621,18 +621,30 @@ private void changeTaskCountInIOConfig(int
desiredActiveTaskCount)
}
/**
- * Clears allocation information including active task groups, partition
groups, partition offsets, and partition IDs.
+ * Clears previous partition assignments in preparation for an upcoming
scaling event.
* <p>
* Note: Does not clear {@link #pendingCompletionTaskGroups} so that the
supervisor remembers that these
* tasks are publishing and auto-scaler does not repeatedly attempt a scale
down until these tasks
* complete. If this is cleared, the next {@link #discoverTasks()} might add
these tasks to
* {@link #activelyReadingTaskGroups}.
+ * <p>
+ * Also does not clear {@link #partitionOffsets} so that the new tasks
remember
+ * where the previous tasks had left off.
+ * <p>
+ * Since both of these are in-memory structures, a change in Overlord
leadership
+ * might cause duplicate scaling actions and/or intermittent task failures
due
+ * to {@code "Inconsistency between stored metadata and target"}.
Review Comment:
It already has a new exception description :)
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