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