siddharthteotia commented on code in PR #9100:
URL: https://github.com/apache/pinot/pull/9100#discussion_r937204103
##########
pinot-query-planner/src/main/java/org/apache/pinot/query/planner/logical/StagePlanner.java:
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@@ -105,30 +113,128 @@ private StageNode walkRelPlan(RelNode node, int
currentStageId) {
RelDistribution.Type exchangeType = distribution.getType();
// 2. make an exchange sender and receiver node pair
- StageNode mailboxReceiver = new MailboxReceiveNode(currentStageId,
nextStageRoot.getDataSchema(),
- nextStageRoot.getStageId(), exchangeType);
- StageNode mailboxSender = new
MailboxSendNode(nextStageRoot.getStageId(), nextStageRoot.getDataSchema(),
- mailboxReceiver.getStageId(), exchangeType, exchangeType ==
RelDistribution.Type.HASH_DISTRIBUTED
- ? new FieldSelectionKeySelector(distributionKeys) : null);
+ KeySelector<Object[], Object[]> keySelector = exchangeType ==
RelDistribution.Type.HASH_DISTRIBUTED
+ ? new FieldSelectionKeySelector(distributionKeys) : null;
Review Comment:
Might want to add a comment here to explain the rationale. Something like
this ?
Basically, we currently support two kinds of exchanges (BROADCAST and
HASH_DISTRIBUTE) via hints. Only in the latter scenario as of now, there is a
case for optimizing the exchange and considering skipping it. If the exchange
type is BROADCAST, we can't avoid exchange and we won't have this situation
because otherwise it becomes sort of colocated partitioned join (which I think
will be added later and should have used a different exchange type through a
different hint). This is why the keySelector is null in the first scenario
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