Default parallel for Pig
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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
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. Eg:
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" keyword.
3. If user put multiple default_parallel inside script, the last entry will be
taken.
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