[jira] Updated: (HIVE-404) Problems in "SELECT * FROM t SORT BY col1 LIMIT 100"

["Carl Steinbach (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HIVE-404?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Carl Steinbach updated HIVE-404:
--------------------------------

        Fix Version/s: 0.3.0
                           (was: 0.4.0)
    Affects Version/s:     (was: 0.3.0)
                           (was: 0.4.0)

> Problems in "SELECT * FROM t SORT BY col1 LIMIT 100"
> ----------------------------------------------------
>
>                 Key: HIVE-404
>                 URL: https://issues.apache.org/jira/browse/HIVE-404
>             Project: Hadoop Hive
>          Issue Type: Bug
>          Components: Query Processor
>            Reporter: Zheng Shao
>            Assignee: Namit Jain
>             Fix For: 0.3.0
>
>         Attachments: hive.404.1.patch, hive.404.2.patch
>
>
> Unless the user specify "set mapred.reduce.tasks=1;", he will see unexpected results with the query of  "SELECT * FROM t SORT BY col1 LIMIT 100"
> Basically, in the first map-reduce job, each reducer will get sorted data and only keep the first 100. In the second map-reduce job, we will distribute and sort the data randomly, before feeding into a single reducer that outputs the first 100.
> In short, the query will output 100 random records in N * 100 top records from each of the reducer in the first map-reduce job.
> This is contradicting to what people expects.
> We should propagate the SORT BY columns to the second map-reduce job.

-- 
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.