Nested UDFs cause _very_ high memory usage when processing query
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Key: HIVE-372
URL: https://issues.apache.org/jira/browse/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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