Add explain plan capabilities to Hive QL
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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
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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