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https://issues.apache.org/jira/browse/PIG-729?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12697638#action_12697638
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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.
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