hadoop - 组合器是否适用于多个映射器的结果？

Question

如果在同一个节点上执行多个映射器，combiner 是否会合并多个映射器的结果？

我在文档或书籍中找不到这个问题的答案。我能找到的组合器示例似乎都有所不同，即使它只能聚合来自一个映射器的结果。

Answer 1

来自雅虎的 Hadoop Tutorial :

The Combiner will receive as input all data emitted by the Mapper instances on a given node. The output from the Combiner is then sent to the Reducers, instead of the output from the Mappers. The Combiner is a "mini-reduce" process which operates only on data generated by one machine.

所以回答你的问题，是的。