Hadoop是一个用于运行应用程序在大型集群的廉价硬件设备上的框架。Hadoop为应用程序透明的提供了一组稳定/可靠的接口和数据运动。在 Hadoop中实现了Google的MapReduce算法，它能够把应用程序分割成许多很小的工作单元，每个单元可以在任何集群节点上执行或重复执行。此外，Hadoop还提供一个分布式文件系统用来在各个计算节点上存储数据，并提供了对数据读写的高吞吐率。由于应用了map/reduce和分布式文件系统使得Hadoop框架具有高容错性，它会自动处理失败节点。已经在具有600个节点的集群测试过Hadoop框架。- Apache Hadoop Core is a software platform that lets one easily write and run applications that process vast amounts of data.



Here s what makes Hadoop especially useful:



　 * Scalable: Hadoop can reliably store and process petabytes.

　 * Economical: It distributes the data and processing across clusters of commonly available computers. These clusters can number into the thousands of nodes.

　 * Efficient: By distributing the data, Hadoop can process it in parallel on the nodes where the data is located. This makes it extremely rapid.

　 * Reliable: Hadoop automatically maintains multiple copies of data and automatically redeploys computing tasks based on failures.



Hadoop implements MapReduce, using the Hadoop Distributed File System (HDFS) (see figure below.) MapReduce divides applications into many small blocks of work. HDFS creates multiple replicas of data blocks for reliability, placing them on compute nodes around the cluster. MapReduce can then process the data w