lucasbru commented on code in PR #20486:
URL: https://github.com/apache/kafka/pull/20486#discussion_r2330103941
##########
group-coordinator/src/main/java/org/apache/kafka/coordinator/group/streams/assignor/StickyTaskAssignor.java:
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@@ -193,6 +196,9 @@ private void assignActive(final Set<TaskId> activeTasks) {
}
}
+ // To achieve an initially range-based assignment, sort by subtopology
+
activeTasks.sort(Comparator.comparing(TaskId::subtopologyId).thenComparing(TaskId::partition));
+
Review Comment:
Yes. I should clarify in the comment that this mostly applies to the case
where the number of partitions is a multiple of the number of nodes, and in
particular the common case where number of partitions = number of nodes.
We assume we start from a pretty balanced assignment (all processes have
roughly equal load). Then, the assignment by-load below is mostly a round-robin
assignment in most situations:
- If we start fresh, all processes have 0 load and we will do a complete
round-robin assignment
- If we scale down, all processes will have roughly the same N load and we
will do roughly round-robin assignment
- If we scale up, we will assign all the tasks that we didnt assign above
to the new nodes. We will do a round-robin assignment among the new nodes.
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