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From "Olga Natkovich (JIRA)" <j...@apache.org>
Subject [jira] Commented: (PIG-895) Default parallel for Pig
Date Tue, 28 Jul 2009 15:58:14 GMT

    [ https://issues.apache.org/jira/browse/PIG-895?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12736116#action_12736116

Olga Natkovich commented on PIG-895:


> Default parallel for Pig
> ------------------------
>                 Key: PIG-895
>                 URL: https://issues.apache.org/jira/browse/PIG-895
>             Project: Pig
>          Issue Type: New Feature
>          Components: impl
>    Affects Versions: 0.3.0
>            Reporter: Daniel Dai
>             Fix For: 0.4.0
>         Attachments: PIG-895-1.patch, PIG-895-2.patch, PIG-895-3.patch
> For hadoop 20, if user don't specify the number of reducers, hadoop will use 1 reducer
as the default value. It is different from previous of hadoop, in which default reducer number
is usually good. 1 reducer is not what user want for sure. Although user can use "parallel"
keyword to specify number of reducers for each statement, it is wordy. We need a convenient
way for users to express a desired number of reducers. Here is my propose:
> 1. Add one property "default_parallel" to Pig. User can set default_parallel in script.
>    set default_parallel '10';
> 2. default_parallel is a hint to Pig. Pig is free to optimize the number of reducers
(unlike parallel keyword). Currently, since we do not have a mechanism to determine the optimal
number of reducers, default_parallel will be always granted, unless it is override by "parallel"
> 3. If user put multiple default_parallel inside script, the last entry will be taken.

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