A port number of 0 instructs the server to start on a free port, but this is generally discouraged because it is incompatible with setting cluster-wide firewall policies.
ECC memory is strongly recommended, as several Hadoop users have reported seeing many checksum errors when using non-ECC memory on Hadoop clusters.
配置成多个路径,FSImage和EditLog会同时写入多个路径,方便以后恢复用
不适合datanode,如果配置成RAID的话,就不需要副本了:
适合namenode:用于保护元数据信息
参数mapreduce.job.reduce.slowstart.completedmaps表示map任务完成多少后,reduce任务才能开始执行。将其设置成0.80,以增加集群的吞吐量
当你实现的java类和Hadoop自带的类相同的时候,怎么处理呢?如果不配置该参数的话,在执行mapreduce作业时,系统会优先选择Hadoop框架中已经存在的java类而不是用户指定包中自己编写的java类