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https://issues.apache.org/jira/browse/HIVE-3550?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Phabricator updated HIVE-3550:
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Attachment: HIVE-3550.D5943.1.patch
navis requested code review of "HIVE-3550 [jira] Early skipping for limit
operator at reduce stage".
Reviewers: JIRA
DPAL-1908 Early skipping for limit operator at reduce stage
Queries with limit clause whose final result is from reduce stage could not
be early exited like map stage. But it seemed possible to just skip remaining
lines. It can be accomplished by adding just two lines. Is there any reason we
should not to do that?
select key from src order by key limit 10;
1. current
ExtractOperator: 3 forwarded 500 rows
LimitOperator: 4 forwarded 10 rows
2. early skipping
ExtractOperator: 3 forwarded 12 rows
LimitOperator: 4 forwarded 10 rows
TEST PLAN
EMPTY
REVISION DETAIL
https://reviews.facebook.net/D5943
AFFECTED FILES
ql/src/java/org/apache/hadoop/hive/ql/exec/ExecReducer.java
MANAGE HERALD DIFFERENTIAL RULES
https://reviews.facebook.net/herald/view/differential/
WHY DID I GET THIS EMAIL?
https://reviews.facebook.net/herald/transcript/14115/
To: JIRA, navis
> Early skipping for limit operator at reduce stage
> -------------------------------------------------
>
> Key: HIVE-3550
> URL: https://issues.apache.org/jira/browse/HIVE-3550
> Project: Hive
> Issue Type: Improvement
> Components: Query Processor
> Reporter: Navis
> Assignee: Navis
> Priority: Trivial
> Attachments: HIVE-3550.D5943.1.patch
>
>
> Queries with limit clause whose final result is from reduce stage could not
> be early exited like map stage. But it seemed possible to just skip remaining
> lines. It can be accomplished by adding just two lines. Is there any reason
> we should not to do that?
> {noformat}
> select key from src order by key limit 10;
> 1. current
> ExtractOperator: 3 forwarded 500 rows
> LimitOperator: 4 forwarded 10 rows
> 2. early skipping
> ExtractOperator: 3 forwarded 12 rows
> LimitOperator: 4 forwarded 10 rows
> {noformat}
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