[jira] [Commented] (TAJO-584) Improve distributed merge sort

["Hyunsik Choi (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TAJO-584?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13891248#comment-13891248 ] 

Hyunsik Choi commented on TAJO-584:
-----------------------------------

Created a review request against branch master in reviewboard 
https://reviews.apache.org/r/17726/


> Improve distributed merge sort
> ------------------------------
>
>                 Key: TAJO-584
>                 URL: https://issues.apache.org/jira/browse/TAJO-584
>             Project: Tajo
>          Issue Type: Improvement
>          Components: distributed query plan, physical operator
>            Reporter: Hyunsik Choi
>            Assignee: Hyunsik Choi
>             Fix For: 0.8-incubating
>
>         Attachments: TAJO-584.patch
>
>
> In Tajo, sort operator is similar to merge sort, but it works in a distributed manner. The first sort phase sorts each fragment in local machine, the intermediate data are shuffled in range partition, and then the the second sort phase in each node sorts the range-partitioned data.
> However, the second sort phase reads all shuffled data via one scanner. It causes performance degrade. This patch improves the second sort phase to merge directly all already-sorted intermediate data. It significantly reduces the response time of sort queries.
> I carried out some simple benchmark with the following query on TPC-H 100GB data sets:
> {code:sql}
> select l_orderkey from lineitem order by l_orderkey;
> {code}
> The lineitem table occupies 75GB. The query response time are dramatically reduced from 480 to 260 secs. This patch exploits the design of TAJO-36. So, this patch requires TAJO-36.



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