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From "Phabricator (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HIVE-3972) Support using multiple reducer for fetching order by results
Date Tue, 05 Feb 2013 08:56:16 GMT

    [ https://issues.apache.org/jira/browse/HIVE-3972?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13571160#comment-13571160
] 

Phabricator commented on HIVE-3972:
-----------------------------------

njain has commented on the revision "HIVE-3972 [jira] Support using multiple reducer for fetching
order by results".

INLINE COMMENTS
  conf/hive-default.xml.template:1621 nit: reducers


  for the last MapReduce task for order by
  ql/src/java/org/apache/hadoop/hive/ql/exec/RowFetcher.java:1 apache header
  ql/src/test/queries/clientpositive/orderby_query_bucketing.q:3 can you perform explain extended
?
  I think, it also shows the number of reducers.
  ql/src/test/queries/clientpositive/orderby_query_bucketing.q:3 Might be easier to create
a tmp table with 10 rows initially to reduce the number of results.
  ql/src/java/org/apache/hadoop/hive/ql/exec/RowFetcher.java:8 Add some comments - it would
be good to have a lot of examples.
  ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java:5604 What happens if it
is -1 ?

  Shouldn't useBucketingForOrderBy be false ?

REVISION DETAIL
  https://reviews.facebook.net/D8349

To: JIRA, navis
Cc: njain

                
> Support using multiple reducer for fetching order by results
> ------------------------------------------------------------
>
>                 Key: HIVE-3972
>                 URL: https://issues.apache.org/jira/browse/HIVE-3972
>             Project: Hive
>          Issue Type: Improvement
>          Components: Query Processor
>            Reporter: Navis
>            Assignee: Navis
>            Priority: Minor
>         Attachments: HIVE-3972.D8349.1.patch, HIVE-3972.D8349.2.patch
>
>
> Queries for fetching results which have lastly "order by" clause make final MR run with
single reducer, which can be too much. For example, 
> {code}
> select value, sum(key) as sum from src group by value order by sum;
> {code}
> If number of reducer is reasonable, multiple result files could be merged into single
sorted stream in the fetcher level.

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