java: add reducer that separates keys and values when map output is pairs
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Key: AVRO-581
URL: https://issues.apache.org/jira/browse/AVRO-581
Project: Avro
Issue Type: New Feature
Components: java
Reporter: Doug Cutting
Assignee: Doug Cutting
Fix For: 1.4.0
We should add a Pair<K,V> class, implementing SpecificRecord, that combines
instances of two schemas (specific or generic). Pairs would be compared by
key, ignoring value. The template for its schema would be:
{code}
{"type": "record", "name": "org.apache.avro.mapred.Pair", "fields":[
{"name": "key", "type":" <<insert key schema here>>},
{"name": "value", "order": "ignore", "type": <<insert value schema>>}
]}
{code}
When map outputs are instances of this class, a reducer may be used whose
reduce method is something like:
public abstract void reduce(K key, Iterable<V> values);
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