Rajkumar Singh created HIVE-19192:

             Summary: HiveServer2 query compilation : query compilation time 
increases sql has multiple unions 
                 Key: HIVE-19192
                 URL: https://issues.apache.org/jira/browse/HIVE-19192
             Project: Hive
          Issue Type: Improvement
          Components: Hive, HiveServer2
    Affects Versions: 2.1.0, 1.2.1
         Environment: Hive-1.2.1


            Reporter: Rajkumar Singh
         Attachments: query-with-100-union.q, query-with-200-union.q, 

query compilation time suffer a lot if SQL has many unions, here is the simple 
reproduce of the problem. PFA attached query with 50,100 and 200 unions(forgive 
me for this bad SQL). when run explain against hiveserver2 I can see the 
compilation time increase many folds.


1,671 rows selected (10.662 seconds)

3,321 rows selected (101.709 seconds)

6,588 rows selected (1074.487 seconds)


Running such SQL against hiveserver2 can starve other SQL to run into single 
threaded compilation stage.

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