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David Ciemiewicz commented on PIG-729: -------------------------------------- Adding switches on the command line versus parameters is harder to maintain for whom? Certainly it is not harder for me to maintain as a user if I say -parallelism than if I have to litter my Pig scripts with PARALLEL=n statements and then have to set other types of parallelism in the numbers of reducers. In fact, doing this properly with command line options makes my life as a developer MUCH easier. If it is "harder to maintain for the Pig development team" well, I think that is a much more scalable burden for someone on the development team to do maintenance than for hundreds or thousands of pig programmers. There's a maxim in business -- the customer is always right. :^) > Use of default parallelism > -------------------------- > > Key: PIG-729 > URL: https://issues.apache.org/jira/browse/PIG-729 > Project: Pig > Issue Type: Bug > Components: impl > Affects Versions: 0.2.1 > Environment: Hadoop 0.20 > Reporter: Santhosh Srinivasan > Fix For: 0.2.1 > > > Currently, if the user does not specify the number of reduce slots using the > parallel keyword, Pig lets Hadoop decide on the default number of reducers. > This model worked well with dynamically allocated clusters using HOD and for > static clusters where the default number of reduce slots was explicitly set. > With Hadoop 0.20, a single static cluster will be shared amongst a number of > queues. As a result, a common scenario is to end up with default number of > reducers set to one (1). > When users migrate to Hadoop 0.20, they might see a dramatic change in the > performance of their queries if they had not used the parallel keyword to > specify the number of reducers. In order to mitigate such circumstances, Pig > can support one of the following: > 1. Specify a default parallelism for the entire script. > This option will allow users to use the same parallelism for all operators > that do not have the explicit parallel keyword. This will ensure that the > scripts utilize more reducers than the default of one reducer. On the down > side, due to data transformations, usually operations that are performed > towards the end of the script will need smaller number of reducers compared > to the operators that appear at the beginning of the script. > 2. Display a warning message for each reduce side operator that does have the > use of the explicit parallel keyword. Proceed with the execution. > 3. Display an error message indicating the operator that does not have the > explicit use of the parallel keyword. Stop the execution. > Other suggestions/thoughts/solutions are welcome. -- This message is automatically generated by JIRA. - You can reply to this email to add a comment to the issue online.