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