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https://issues.apache.org/jira/browse/HDFS-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068448#comment-13068448
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Konstantin Shvachko commented on HDFS-2141:
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Guys, you are changing the meaning of the role and calling it state. I
intentionally tried to avoid using "state" while designing BackupNode, because
word state is highly overloaded.
Yes original NameNode was not designed for HA, but BackupNode was. Therefore
the roles.
Please read here:
"[Standby node (SN) - a name-node in "standby"
state.|https://issues.apache.org/jira/secure/attachment/12400631/StreamEditsToBN.pdf]
Standby is a backup node, which is able to take over the active role if the
current active fails."
Role is not a name of the daemon its the what defines the functionality of NN.
NN functions as single active node, but cannot checkpoint. BN keeps the copy of
the namepsace, but cannot turn into standby. CN creates checkpoints but does
not keep the namespace. SBN can turn into Active.
What is wrong with current terminology and why it needs to be changed?
Todd, could we please stay on the topic and not diverge to inheritance issues.
I agree NN should evolve into a single class for all nodes, but lets do it
somewhere else.
> 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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