创建了多少映射器类实例？

Question

如果我有一个名为MAxTemperatureMapper的映射器类，并且当我将带有100条记录的文件的TextInputFormat类作为输入时。 是创建的映射器实例的数量等于输入拆分的数量，还是为输入中的每个键值对创建的新映射器。？

Answer 1

Number of mapper would be equal to number of input splits .

when ever you submit a job ,first of all it determines number of splits ,splits are logical .

usually one split size is equal to hdfs block size but that can also be configured where your split size could be less than or greater than block size . for efficent processing usually one split size is equal to block size .

suppose you  have file of 1 GB ,your default block size is 128 mb so approximately you will have 8  blocks and 8 input splits would be required and hence 8 mappers would be invoked for this process .