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From "Steve Corona (JIRA)" <>
Subject [jira] Created: (HIVE-372) Nested UDFs cause _very_ high memory usage when processing query
Date Thu, 26 Mar 2009 15:42:15 GMT
Nested UDFs cause _very_ high memory usage when processing query

                 Key: HIVE-372
             Project: Hadoop Hive
          Issue Type: Bug
          Components: Query Processor
         Environment: Fedora Linux, 10x Amazon EC2 (Large Instance w/ 8GB Ram)
            Reporter: Steve Corona

When nesting UDFs, the Hive Query processor takes a large amount of time+memory to process
the query. For example, I ran something along the lines of:

select trim( trim( trim(trim( trim( trim( trim( trim( trim(column))))))))) from test_table;

This query needs 10GB+ of memory to process before it'll launch the job. The amount of memory
increases exponentially with each nested UDF.

Obviously, I am using trim() in this case as a simple example that causes the same problem
to occur. In my actual use-case I had a bunch of nested regexp_replaces.

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