combine operation is understood to reduce the map in the combined operation of the output end of a single map data task
effects:
reduce the amount of data transmitted to Reduce in. It is mainly to reduce output Mapper thereby reducing the load on network bandwidth and Reducer
disadvantages:
combine optimization as a means of options, not all are suitable for MR procedures combine
the appropriate scene: for example seeking maximum, sum, for example, an intermediate value not seek
Mapreduce use and errors in Combiner
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Origin blog.csdn.net/wj1298250240/article/details/103965231
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