java - 二级名称节点和被动名称节点有什么区别

Question

我们在 namenode 的高可用性中使用的另一个 namenode 是什么，我很困惑在 hadoop 联合中使用的其他 namenode 是什么

Answer 1

Hope this information solves your confusion

1)Namenode::

Namenode holds the meta data for the HDFS Namespaceinformation, block information etc. Namenode stores the HDFSfilesystem information in a file named fsimage. Updates to the filesystem (add/remove blocks) are not updating the fsimage file , it willbe appended to the edit log, Fsimage contains mapping of blocks tofiles and other file system properties called snapshot of namenode. When restaring, the namenode reads thefsimage and then applies all the changes from the log file to bringthe filesystem state up to date in memory.

2)Secondary Namenode::

The secondary namenode periodically pulls thesetwo(Edits nd fsimage) files, and the namenode starts writing changes to a new editsfile. Then, the secondary namenode merges the changes from the editsfile with the old snapshot from the fsimage file and creates anupdated fsimage file. This updated fsimage file is then copied to thenamenode.

3)FailOver NameNode or Passive Namenode(Only if HA enabled):: Prior toHadoop 2.0.0, the NameNode was a single point of failure (SPOF) in anHDFS cluster. Each cluster had a single NameNode, and if that machineor process became unavailable, the cluster as a whole would beunavailable until the NameNode was either restarted or brought up on aseparate machine. the above problems is addressed by providing the option of running two redundant NameNodes in an HA cluster, the Standby/Passive NameNode also performscheckpoints of the namespace state, and thus it is not necessary torun a Secondary NameNode, CheckpointNode, or BackupNode in an HAcluster. In fact, to do so would be an error.