siddharthteotia commented on code in PR #8558:
URL: https://github.com/apache/pinot/pull/8558#discussion_r855374289
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pinot-query-planner/src/main/java/org/apache/pinot/query/planner/StagePlanner.java:
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@@ -67,11 +68,12 @@ public QueryPlan makePlan(RelNode relRoot) {
StageNode globalStageRoot = walkRelPlan(relRoot, getNewStageId());
// global root needs to send results back to the ROOT, a.k.a. the client
response node.
- // the last stage is always a broadcast-gather.
+ // the last stage only has one receiver so doesn't matter what the
exchange type is.
Review Comment:
I agree that the last exchange at the top (between sender(s) in 1st stage
and single receiver in 0th stage) can be anything. May be
RelDistribution.Type.ANY is more suitable ?
Slightly related question - I think exchange type information is enough to
decide the kind of sender (like right now it will be broadcast, later it could
be shuffle / hash partition exchange). How do we decide the kind of exact
receiver ? Especially for the receiver in the root stage, we ideally want to
know if the receiver is unordered or ordered for simple v/s sorted merge
respectively ?
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