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https://issues.apache.org/jira/browse/CRUNCH-235?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13700935#comment-13700935
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Tom White commented on CRUNCH-235:
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The TaskAttemptContext stuff is a problem, but it should only be a problem for
Crunch itself, not for Crunch apps. This change would help a bit by removing
the leakage of incompatible classes into Crunch apps. I agree that you'd have
to select the right Crunch JAR, although that could be done at runtime, without
any recompilation.
I did look to see whether the approach we recently used in Parquet to produce a
single JAR would work in Crunch
(https://github.com/Parquet/parquet-mr/pull/32#issuecomment-17283008), but as
you point out, the Crunch code is too performance critical to use the
reflection-based approach there. In Parquet it's not a problem since it's only
per-task or per-job calls to get Configuration that need to be done
reflectively. In Crunch, OutputEmitter calls write() for every record, so it's
not a good candidate for reflection.
> Avoid exposing incompatible Hadoop classes in Crunch API
> --------------------------------------------------------
>
> Key: CRUNCH-235
> URL: https://issues.apache.org/jira/browse/CRUNCH-235
> Project: Crunch
> Issue Type: Improvement
> Components: Core
> Reporter: Tom White
> Assignee: Tom White
> Attachments: CRUNCH-235.patch
>
>
> Between Hadoop 1 and 2, org.apache.hadoop.mapreduce.Counter changed from a
> class to an interface. Therefore, exposing Counter in Crunch's API means that
> Crunch programs may need to be recompiled when moving from a Hadoop 1 to a
> Hadoop 2 cluster. It would be nice to avoid the need to recompile.
> Note that Crunch itself has two artifacts - one for each major version of
> Hadoop - and the change proposed here would not alter that, it would just
> mean that the same Crunch program binary could be used with either Crunch
> artifact.
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