Github user hyunsik commented on a diff in the pull request:
https://github.com/apache/tajo/pull/583#discussion_r31093213
--- Diff:
tajo-core/src/main/java/org/apache/tajo/engine/planner/global/ExecutionBlock.java
---
@@ -39,8 +40,38 @@
private boolean hasJoinPlan;
private boolean hasUnionPlan;
-
- private Set<String> broadcasted = new HashSet<String>();
+ private boolean isUnionOnly;
+
+ private Map<String, ScanNode> broadcastRelations = TUtil.newHashMap();
+
+ /*
+ * An execution block is null-supplying or preserved-row when its output
is used as an input for outer join.
+ * These flags are set according to the type of outer join.
+ * Here are brief descriptions for these flags.
+ *
+ * 1) left outer join
+ *
+ * left outer join
+ * / \
+ * preserved-row null-supplying
+ *
+ * 2) right outer join
+ *
+ * right outer join
+ * / \
+ * null-supplying preserved-row
+ *
+ * 3) full outer join
+ *
+ * full outer join
+ * / \
+ * null-supplying preserved-row
+ * preserved-row null-supplying
+ *
+ * The null-supplying and preserved-row flags are used to find which
relations will be broadcasted.
+ */
+ protected transient boolean nullSuppllying = false;
--- End diff --
'transient' seems to be not necessary.
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