[GitHub] [hive] okumin commented on a diff in pull request #4363: HIVE-24606: Multi-stage materialized CTEs can lose intermediate data

["okumin (via GitHub)" <gi...@apache.org>]

okumin commented on code in PR #4363:
URL: https://github.com/apache/hive/pull/4363#discussion_r1207584190


##########
ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java:
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@@ -1440,47 +1443,78 @@ public String toString() {
     }
   }
 
-  private List<Task<?>> toRealRootTasks(List<CTEClause> execution) {
-    List<Task<?>> cteRoots = new ArrayList<>();
-    List<Task<?>> cteLeafs = new ArrayList<>();
-    List<Task<?>> curTopRoots = null;

Review Comment:
   This looks like the root cause. In [the case I put in the ticket](https://issues.apache.org/jira/browse/HIVE-24606), there are the following dependencies.
   
   - `<root> -> a1`
   - `<root> -> x`
   - `<root> -> a2`
   - `a2 -> a1`
   
   But the old implementation tries to traverse CTEs in order of `a1` -> `x` -> `a2` -> `<root>`, following the appearance of AST.
   As a result, when it visits `a2`, the information of `a1` has gone and it fails to link `a2` with `a1`.



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