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Date: Fri, 3 Aug 2012 07:35:02 +0000 (UTC)
From: "Rahul Sharma (JIRA)" <jira@apache.org>
To: crunch-dev@incubator.apache.org
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Subject: [jira] [Updated] (CRUNCH-23) PCollection#sort doesn't do a full
 sort on values
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     [ https://issues.apache.org/jira/browse/CRUNCH-23?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Rahul Sharma updated CRUNCH-23:
-------------------------------

    Attachment: 0001-CRUNCH-23-fix-sorting.patch

Josh, I have implemented the same solution. But I feel that the data distribution is not perfect there. 

The solution is based on reservoir sampling. So the keys that are used in the Partioner are selected from a subset of the data. It solely depends on how good is the subset sample.  
                
> PCollection#sort doesn't do a full sort on values
> -------------------------------------------------
>
>                 Key: CRUNCH-23
>                 URL: https://issues.apache.org/jira/browse/CRUNCH-23
>             Project: Crunch
>          Issue Type: Bug
>            Reporter: Gabriel Reid
>            Assignee: Rahul Sharma
>         Attachments: 0001-CRUNCH-23-fix-sorting.patch, CRUNCH-23-used-TotalOrderpartioner-for-sorting-keys.patch, SortTest.java
>
>
> When a PCollection is sorted (using PCollection#sort), the sorting that is performed is only per reducer, and not an absolute sort over all values. This means that the values are not in sorted order if they are iterated over on a materialized collection. It also means that the sorted files that are output from a sort operation can not be simply concatenated to come to a single sorted file.

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