hadoop namenode java.lang.OutOfMemoryError: GC overhead limit exceeded
详细信息：
ERROR org.apache.hadoop.hdfs.server.namenode.NameNode: Failed to start namenode.
java.lang.OutOfMemoryError: GC overhead limit exceeded
原因，heapsize默认1000，不够用！
vi /opt/hadoop-2.7.4/etc/hadoop/hadoop-env.sh
export HADOOP_HEAPSIZE=5120 修改为合适的值
