The shuffle process is the core of MapReduce, also known as the place where miracles occur. To understand mapreduce, shuffle must be understood. The normal meaning of shuffle is shuffling or cluttering, and perhaps more familiar is the Java API
IV. For details about map tasks, see
V. Reduce task details
Vi. Distributed support
2. Distributed Computing (MAP/reduce)
Distributed Computing is also a broad concept. In this case, it refers
Two . Distributed Computing ( Map/reduce )Distributed computing, too, is a broad concept, where it narrowly refers to a distributed framework designed by the Google Map/reduce framework. In Hadoop, distributed file systems, to a large extent, are
Shuffle describes the process of data from the map task output to the reduce task input.Personal Understanding:The results of map execution are saved as a local file:As long as map execution is complete, the in-memory map data will be saved to the
Recently, a complicated SQL statement was executed, and a pile of small files appeared during file output:
To sum up a sentence for merging small files, we can conclude that the number of files is too large, increasing the pressure on namenode.
MongoDB: Map-Reduce, mongodbmap-reduce
Map-reduce is a data processing program (paradigm) that considers large data to obtain useful aggregation results. For map-reduce operations, MongoDB provides mapreduce commands.
Consider the following
Hadoop is an open source system that implements Google's cloud computing system, including parallel computing model Map/reduce, Distributed File System HDFs, and distributed database HBase, along with a wide range of Hadoop related
Read this article please go out to run two laps, and then brew a pot of tea, while drinking tea, while watching, after reading you on the whole of Hadoop understand.about HadoopHadoop is an open source system that implements Google's cloud computing
From: http://blog.csdn.net/opennaive/article/details/75141461. mapreduce did not find Google, so I want to use a hadoop project structure to describe the position of mapreduce, as shown in. Hadoop is actually an open-source implementation of Google
Map-reduce is a data processing program (paradigm) that considers large data to obtain useful aggregation results ). for map-reduce operations, MongoDB provides mapreduce commands. consider the following map-reduce operation: in MongoDB, the
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