Github user jihoonson commented on a diff in the pull request:
https://github.com/apache/tajo/pull/402#discussion_r26217412
--- Diff:
tajo-core/src/main/java/org/apache/tajo/engine/planner/global/GlobalPlanner.java
---
@@ -1371,32 +1373,57 @@ public LogicalNode visitUnion(GlobalPlanContext
context, LogicalPlan plan, Logic
LogicalPlan.QueryBlock rightQueryBlock =
plan.getBlock(node.getRightChild());
LogicalNode rightChild = visit(context, plan, rightQueryBlock,
rightQueryBlock.getRoot(), stack);
stack.pop();
+
+ MasterPlan masterPlan = context.getPlan();
List<ExecutionBlock> unionBlocks = Lists.newArrayList();
List<ExecutionBlock> queryBlockBlocks = Lists.newArrayList();
ExecutionBlock leftBlock =
context.execBlockMap.remove(leftChild.getPID());
ExecutionBlock rightBlock =
context.execBlockMap.remove(rightChild.getPID());
+
+ boolean leftUnion = (leftChild.getType() == NodeType.TABLE_SUBQUERY)
&&
+ (((TableSubQueryNode)leftChild).getSubQuery().getType() ==
NodeType.UNION);
+ boolean rightUnion = (rightChild.getType() ==
NodeType.TABLE_SUBQUERY) &&
+ (((TableSubQueryNode)rightChild).getSubQuery().getType() ==
NodeType.UNION);
if (leftChild.getType() == NodeType.UNION) {
unionBlocks.add(leftBlock);
} else {
- queryBlockBlocks.add(leftBlock);
+ if (leftUnion) {
+ node.setLeftChild(
+ createScanNodeWithTableSubQuery(masterPlan,
--- End diff --
Please check whether I understand your patch well.
When an union has a child of subquery that has another union child, the
subquery and its child union should be removed. Let me suppose an example union
```u1```. It has a child subquery ```s1``` which has another union child,
```u2```. Finally, ```u2``` has a scan child, ```scan1```. In this case,
```u1``` should be directly connected with ```scan```.
However, according to your patch, the example query forms (```scan1``` -
```u2``` - ```s1```) - (```scan2``` - ```u1```). Parentheses mean query blocks,
and ```scan2``` is created at this line. In this case, I think that it is
difficult to avoid unnecessary materialization of intermediate data between
query blocks.
If I misunderstand something, please tell me.
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