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https://issues.apache.org/jira/browse/HIVE-3562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13527803#comment-13527803
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Phabricator commented on HIVE-3562:
-----------------------------------
tarball has requested changes to the revision "HIVE-3562 [jira] Some limit can
be pushed down to map stage".
INLINE COMMENTS
conf/hive-default.xml.template:1407 Why is optimization disabled by default?
This is good stuff and should be switched on!
conf/hive-default.xml.template:1413 10 million seems like a really large
threshold. Maybe in the 50k range?
ql/src/java/org/apache/hadoop/hive/ql/exec/ReduceSinkOperator.java:378 The
current implementation doesn't look like a heap to me. Why not simply use
java.util.PriorityQueue?
ql/src/java/org/apache/hadoop/hive/ql/exec/ReduceSinkOperator.java:383
Shouldn't nulls be equal to each other?
ql/src/java/org/apache/hadoop/hive/ql/exec/ReduceSinkOperator.java:379 Better
name? TopNHeap?
REVISION DETAIL
https://reviews.facebook.net/D5967
BRANCH
DPAL-1910
To: JIRA, tarball, navis
Cc: njain
> Some limit can be pushed down to map stage
> ------------------------------------------
>
> Key: HIVE-3562
> URL: https://issues.apache.org/jira/browse/HIVE-3562
> Project: Hive
> Issue Type: Bug
> Reporter: Navis
> Assignee: Navis
> Priority: Trivial
> Attachments: HIVE-3562.D5967.1.patch, HIVE-3562.D5967.2.patch
>
>
> Queries with limit clause (with reasonable number), for example
> {noformat}
> select * from src order by key limit 10;
> {noformat}
> makes operator tree,
> TS-SEL-RS-EXT-LIMIT-FS
> But LIMIT can be partially calculated in RS, reducing size of shuffling.
> TS-SEL-RS(TOP-N)-EXT-LIMIT-FS
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