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Chad Urso McDaniel commented on CRUNCH-192:
-------------------------------------------
Looks good to me.
> Document and enforce the semantics around reducer-based Iterables
> -----------------------------------------------------------------
>
> Key: CRUNCH-192
> URL: https://issues.apache.org/jira/browse/CRUNCH-192
> Project: Crunch
> Issue Type: Bug
> Reporter: Gabriel Reid
> Assignee: Gabriel Reid
> Fix For: 0.6.0
>
> Attachments: CRUNCH-192.patch, CRUNCH-192.patch.v2, CRUNCH-192.patch.v3
>
>
> As reported on user@crunch.apache.org by Chad Urso McDaniel:
> BLUF: The Iterable parameter to CombineFn.process implies you can iterate multiple times
when you cannot and this leads to surprising behavior.
> As many of you probably know, the signature of CombineFn.process is
> ---
> process(Pair<K, Iterable<V>> input, Emitter<Pair<K, V>> emitter)
> ---
> The corresponding Hadoop Reducer signature is
> ---
> reduce(K2 key, Iterator<V2> values, OutputCollector<K3,V3> output, Reporter
reporter)
> ---
> I assume the Crunch use of Iterable is for convenient use in "for" loops.
> Unfortunately, the behavior of this Iterable seems to return the same Iterator object
each time Iterable.iterator() is called.
> This makes sense to me based on the underlying hadoop mapreduce, but violates what I
think most expect from the Iterable interface.
> I understand that it's too late to change the interface, but could we at least have an
javadoc or an exception thrown if the Iterable is used more than once?
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