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Daniel Dai updated PIG-895: --------------------------- Attachment: PIG-895-3.patch Modified the patch according to Alan's suggestion. It is better to use "mapred.reduce.tasks" mechanism to set the default parallel. "default_parallel" setting in Pig will map to "mapred.reduce.tasks" in hadoop. Now we have "parallel" keyword, "default_parallel", and "mapred.reduce.tasks" to determine the number of reducers. The priority from the higher to lower is: 1. parallel keyword 2. default_parallel 3. "mapred.reduce.tasks" setting in hadoop The higher priority setting overrides lower priority setting. > 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. 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. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.