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https://issues.apache.org/jira/browse/PIG-1306?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Yan Zhou updated PIG-1306:
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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, 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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