Jackie-Jiang commented on code in PR #12276:
URL: https://github.com/apache/pinot/pull/12276#discussion_r1459888168
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pinot-broker/src/main/java/org/apache/pinot/broker/routing/instanceselector/MultiStageReplicaGroupSelector.java:
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@@ -86,7 +87,16 @@ Pair<Map<String, String>, Map<String, String>>
select(List<String> segments, int
SegmentStates segmentStates, Map<String, String> queryOptions) {
// Create a copy of InstancePartitions to avoid race-condition with
event-listeners above.
InstancePartitions instancePartitions = _instancePartitions;
- int replicaGroupSelected = requestId %
instancePartitions.getNumReplicaGroups();
+ int replicaGroupSelected;
+ if (_useStickyRouting) {
+ // When using sticky routing, we want to iterate over the
instancePartitions in order to ensure deterministic
+ // selection of replica group across queries i.e. same instance replica
group id is picked each time.
+ // Since the instances within a selected replica group are iterated in
order, the assignment within a selected
+ // replica group is guaranteed to be deterministic.
+ replicaGroupSelected = 0;
Review Comment:
Good point. IIRC we are not using this selector, so both 2 and 3 (1 breaks
the contract which is not okay) are fine. If we go with 2, let's add a note
describing the potential hotspot problem, or we go with 3 and add a todo
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