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https://issues.apache.org/jira/browse/MAPREDUCE-5176?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13662330#comment-13662330
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Carlo Curino commented on MAPREDUCE-5176:
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Karthik, I think there are several other annotations we might want to think
about. @Stateless is one, another one is @PreserveKeyOrder which can express
for example that maps are not messing with sort order and would allow a smart
runtime to pipeline maps and reduces (and skip shuffling) when the input is
sorted. I think this could be a powerful tool to expose opportunities for
runtime optimization which are not possible in the general case (unless you
know something about the code semantics).
If none disagree, I like the idea to have this in a common place (maybe
yarn-common as Karthik suggested?).
BTW I think we are in a great spot to carry along this conversation, since we
have one very specific example of these annotations: @Preemptable for which we
have the entire end-to-end usage scenario (all the preemption in mapreduce
stuff tracked in MAPREDUCE-5189, MAPREDUCE-5192, MAPREDUCE-5194,
MAPREDUCE-5196, MAPREDUCE-5197 and few upcoming ones), and plenty more ideas
coming up from people.
Ideally I would like to move forward with the @Preemptable one and see it
through (so we can evaluate it and learn from it), and in parallel we can
initiate a broader (and rightfully longer) conversation around annotations for
runtime-optimization.
Sandy, what we envisioned for mapreduce is that and advanced user that have a
stateful UDF can mark it as @Preemptable and override the default save to
checkpoint logic to include the portion of state he/she cares about.
> Preemptable annotations (to support preemption in MR)
> -----------------------------------------------------
>
> Key: MAPREDUCE-5176
> URL: https://issues.apache.org/jira/browse/MAPREDUCE-5176
> Project: Hadoop Map/Reduce
> Issue Type: Improvement
> Components: mrv2
> Reporter: Carlo Curino
> Assignee: Carlo Curino
> Attachments: MAPREDUCE-5176.1.patch, MAPREDUCE-5176.patch
>
>
> Proposing a patch that introduces a new annotation @Preemptable that
> represents to the framework property of user-supplied classes (e.g., Reducer,
> OutputCommiter). The intended semantics is that a tagged class is safe to be
> preempted between invocations.
> (this is in spirit similar to the Output Contracts of [Nephele/PACT |
> https://stratosphere.eu/sites/default/files/papers/ComparingMapReduceAndPACTs_11.pdf])
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