From the official document of Backup Node?? it Says: The Backup node does not need to download fsimage and edits files from the active NameNode in order to create a checkpoint, as would be required with a Checkpoint node or Secondary NameNode, since it already has an up-to-date state of the namespace state in memory. I noticed the keyword \'does not need\' ??it gives no clear information about whether or not the Backup Node will download fsimage and edits files from the active NameNode like checkpoint node.
I checked the source code , namely org.apache.hadoop.hdfs.server.namenode.Checkpointer?? I find that Both Backup Node and Checkpoint Node will download fsimage and edits files from active NameNode??no difference. So , although it is unnecessary for Backup Node to download downlaod fsimage and edits files from the active NameNode because it keeps a journal stream from the active name node, but in fact Backup Node still do so. Right? Thanks.
