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From "Yan Zhou (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-1306) [zebra] Support of locally sorted input splits
Date Thu, 25 Mar 2010 17:07:27 GMT

     [ https://issues.apache.org/jira/browse/PIG-1306?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Yan Zhou updated PIG-1306:
--------------------------

    Attachment: PIG-1306.patch

> [zebra] Support of locally sorted input splits
> ----------------------------------------------
>
>                 Key: PIG-1306
>                 URL: https://issues.apache.org/jira/browse/PIG-1306
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Yan Zhou
>            Assignee: Yan Zhou
>             Fix For: 0.7.0
>
>         Attachments: PIG-1306.patch, PIG-1306.patch
>
>
> Current Zebra supports sorted or unsorted input splits on sorted table or sorted table
unions. The sorted input splits are based upon key ranges which do not overlap. And the splits
are basically globally sorted in that they are locally sorted, and their key ranges do not
overlap.
> The biggest problem of the key-range splits are performance hits suffered if data skew
is present, particularly if a key range contains a duplicate key solely which makes the data
trunk of the duplicate keys virtually unsplittable regardless how many mappers are available:
it just has to be processed by a single mapper.
> On the other hand, there are scenarios when the globally sorted splits are a over-kill
and only locally sorted splits are good enough. Examples are the use of Zebra sorted tables
as the probe table in a map-side merge inner join.

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