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From "Suresh Srinivas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2141) Remove NameNode roles Active and Standby (they become states)
Date Tue, 19 Jul 2011 23:29:57 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068066#comment-13068066
] 

Suresh Srinivas commented on HDFS-2141:
---------------------------------------

bq. Seems like you want to introduce a state in addition to the role, so that a daemon in
role NN could have two states active and standby. This IS really confusing to me.
I am not sure what the confusion is. Active and standby are truly states of the namenode.
Depending on the state a namenode is in, the same process/daemon performs different function.
It can change this state during failover without restarting. Irrespective of which state it
is in, it is still the namenode.

bq. We used to say that we start NameNode in active, backup, or checkpoint role. Active is
the default, if you do not specify the role.
Just because checkpoint or backup used Namenode code, they are not namenodes. They provide
entirely different functionality from namenode. Without a restart they cannot take over the
role of the namenode (at least currently!). Hence they are roles a process/daemon started
with and not the states.

I had commented in HADOOP-4529 about not making a separate class for BackupNode. What I am
proposing is:
NameNode running as active or standby. One single code base for Namenode with just two states.

This is different from:
Namenode running as active or goes back to safemode and BackupNode running as backup or active,
as done in HDFS-2064. These are issues I see:
# Unnecessary duplication of "active" state code between Namenode and BackupNode.
# If you also support the functionality of Namenode going from active to standby (currently
HDFS-2064 does not), duplication of "backup" state code between Namenode and BackupNode.

That leaves me a question - what is BackupNode? Why should it be distinct from Namenode.

> 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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