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From "Zheng Shao (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HIVE-372) Nested UDFs cause _very_ high memory usage when processing query
Date Fri, 10 Apr 2009 22:14:14 GMT

    [ https://issues.apache.org/jira/browse/HIVE-372?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12697999#action_12697999
] 

Zheng Shao commented on HIVE-372:
---------------------------------

The patch is mainly for fixing the long-query problem - like 80-union query and this long-udf
query.

The error message is kind of a side effect - and overall we are seeing more error messages
(Just see all the changed error messages in the diff)

We could also do a more thorough fix of the grammar, but that will potentially take much longer,
and it may not be that prioritized compared wtih other to-do items.


> Nested UDFs cause _very_ high memory usage when processing query
> ----------------------------------------------------------------
>
>                 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
>         Attachments: HIVE-372.1.patch, HIVE-372.2.patch
>
>
> 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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