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https://issues.apache.org/jira/browse/HDFS-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068604#comment-13068604
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Konstantin Shvachko commented on HDFS-2141:
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Here is another citation from the document we both authored:
"[The NameNode in HDFS, in addition to its primary role serving client
requests, can alternatively execute either of two other roles, either a
CheckpointNode or a BackupNode. The role is specified at the node
startup...|http://www.aosabook.org/en/hdfs.html]"; Go to Chapter 9.2.5.
> Are all these namenodes? If there is STANDBY already what is the role of
> BACKUP?
Yes they are all NameNodes according to the definition we just published this
month.
The role of BackupNode is to keep the up-to-date namespace in memory, serve
read requests and make checkpoints.
Standby does not currently exist. You know all of it.
So I would propose to keep the roles as they are and introduce states when
necessary, provided the documentation is in place. Building a machine handling
2 states sounds unreasonable.
Can you live with roles, without renaming 2 of them into states? I think it is
an unnecessary change in terminology, which involved code change.
> Remove NameNode roles Active and Standby (they become states)
> -------------------------------------------------------------
>
> Key: HDFS-2141
> URL: https://issues.apache.org/jira/browse/HDFS-2141
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: name-node
> Reporter: Suresh Srinivas
> Assignee: Suresh Srinivas
> Fix For: 0.23.0
>
> Attachments: HDFS-2141.1.patch, HDFS-2141.patch
>
>
> In HDFS, following roles are supported in NameNodeRole: ACTIVE, BACKUP,
> CHECKPOINT and STANDBY.
> Active and Standby are the state of the NameNode. While Backup and CheckPoint
> are the name/role of the daemons that are started. This mixes up the run time
> state of NameNode with the daemon role. I propose changing the NameNodeRole
> to: NAMENODE, BACKUP, CHECKPOINT. HDFS-1974 will introduce the states active
> and standby to the daemon that is running in the role NAMENODE.
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