wutiangan commented on a change in pull request #3886:
URL: https://github.com/apache/incubator-doris/pull/3886#discussion_r440596171
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File path: fe/src/main/java/org/apache/doris/planner/DistributedPlanner.java
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@@ -294,6 +294,11 @@ private PlanFragment createHashJoinFragment(HashJoinNode
node, PlanFragment righ
// broadcast: send the rightChildFragment's output to each node
executing
// the leftChildFragment; the cost across all nodes is proportional to
the
// total amount of data sent
+
+ // NOTICE(cmy): for now, only MysqlScanNode and OlapScanNode has
Cardinality. And MysqlScanNode's Cardinality
+ // is always 0. Other ScanNode's cardinality is -1, so they won't be
able the calculate the cost of
Review comment:
```suggestion
// is always -1. Other ScanNode's cardinality is greater than or
equal to zero, so they won't be able to calculate the cost of
```
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