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https://issues.apache.org/jira/browse/HADOOP-4084?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12631466#action_12631466
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Namit Jain commented on HADOOP-4084:
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Overall, looks good - just some minor comments.
LoadSemanticAnalyzer: line 32/33 - nitpick: remove commented import
ExplainSemanticAnalyzer (line 47): not needed
explain.java: no apache license header on top of file
DDLWork.java: why display name only for create table ? why not for other DDLs
MapRedTask: (line 91) remove explain()
MoveTask: remove explain()
> Add explain plan capabilities to Hive QL
> ----------------------------------------
>
> Key: HADOOP-4084
> URL: https://issues.apache.org/jira/browse/HADOOP-4084
> Project: Hadoop Core
> Issue Type: New Feature
> Components: contrib/hive
> Reporter: Ashish Thusoo
> Assignee: Ashish Thusoo
> Attachments: patch-4084
>
>
> Adding explain plan for queries in hive.
> The current proposal is to support something like:
> EXPLAIN [EXTENDED]
> SELECT ....
> This will output the following:
> Abstract Syntax Tree:
> Number of Stages:
> Dependencies between Stages:
> Plan for each stage:
> If EXTENDED keyword is used then much more information will be emitted where
> as without that keyword only logical information will be emitted.
> e.g. In case of a group by query
> EXPLAIN
> SELECT T.c1, count(1) FROM T GROUP BY T.c1;
> The explain plan itself has two stages
> Stage1 and Stage2
> Stage1 will have the plan for generating the partial aggregates
> and Stage2 will have the plan for generating the complete aggregates.
> I also plan to convert the parse and semantic analysis tests so that they use
> this for finding differences in the plan instead of the programmatic plan
> dumps that we are using today (tests/queries/positive).
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