Hi Chad, Good point -- I know that this has tripped people up in the past. I think that definitely documenting this and possibly enforcing it sounds like a good idea -- I've logged a ticket in JIRA (with the content of your mail), see https://issues.apache.org/jira/browse/CRUNCH-192
- Gabriel On 05 Apr 2013, at 21:30, Chad Urso McDaniel <[email protected]> wrote: > 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?
