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From "Sriranjan Manjunath (JIRA)" <j...@apache.org>
Subject [jira] Updated: (PIG-792) PERFORMANCE: Support skewed join in pig
Date Wed, 22 Jul 2009 09:13:14 GMT

     [ https://issues.apache.org/jira/browse/PIG-792?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Sriranjan Manjunath updated PIG-792:
------------------------------------

    Attachment: skewedjoin.patch

I have attached a patch with most of the suggested modifications. I am still using NullablePartitionWritable
instead of a Tuple since it provides a cleaner approach by using an adapter class and we don't
have to check for the position of the keys in multiple places.

Please ignore the findbugs warning for taking an absolute value of a hashcode. I use it as
an array index and hence need the absolute value.

> PERFORMANCE: Support skewed join in pig
> ---------------------------------------
>
>                 Key: PIG-792
>                 URL: https://issues.apache.org/jira/browse/PIG-792
>             Project: Pig
>          Issue Type: Improvement
>            Reporter: Sriranjan Manjunath
>         Attachments: skewedjoin.patch
>
>
> Fragmented replicated join has a few limitations:
>  - One of the tables needs to be loaded into memory
>  - Join is limited to two tables
> Skewed join partitions the table and joins the records in the reduce phase. It computes
a histogram of the key space to account for skewing in the input records. Further, it adjusts
the number of reducers depending on the key distribution.
> We need to implement the skewed join in pig.

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