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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2141) Remove NameNode roles Active and Standby (they become states)
Date Wed, 20 Jul 2011 20:18:57 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068604#comment-13068604

Konstantin Shvachko commented on HDFS-2141:

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
> 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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