[
https://issues.apache.org/jira/browse/HIVE-3562?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13563464#comment-13563464
]
Phabricator commented on HIVE-3562:
-----------------------------------
navis has commented on the revision "HIVE-3562 [jira] Some limit can be pushed
down to map stage".
I'm also confusing about GBY cases. I mean group by query with "no ordering"
clause, for example,
select key,count(value) from src group by key limit 10;
I think top-K is still applicable. If key is ranged from K1 to K100, all
values for K1~K10 from any mapper are transferred to reducer, which makes valid
result. Isn't it?
And for changing threshold from memory to row count, map aggregation would be
a good example, which is using memory percent. I also think current
implementation is too clumsy, but general direction is right.
REVISION DETAIL
https://reviews.facebook.net/D5967
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,
> HIVE-3562.D5967.3.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
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
