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https://issues.apache.org/jira/browse/HDFS-2141?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068680#comment-13068680
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Sanjay Radia commented on HDFS-2141:
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>SBN can turn into Active.
Looks like you have BN and SBN and perhaps ABN when the SBN turns active.
Both ABN and Active NN both provide the same active function. This seems
confusing.
Also you forgot to respond to
>You seem to suggest that backup NN is the only way to be in standby mode i.e.
>2b; but 2a is an equally valid
>way to perfrom the standby function.
There is another service where a standby reads edits from shared storage.
Let me use a neutral term for the purposes of this discussion (I will call this
mode for this discussion - we can then we can decide the terminology about
whether to call this role or state or something else).
# Mode Active: A NN running as active
# Mode Standby: A NN running as standby and it keeps in sync with the active
using one of two methods
** a) syncing from the active via shared storage
** b) syncing from the active via direct edits stream (as done in the backup NN
code)
NN in standby mode has to run a special service to keep its state hot = it
uses (2a) or (2b).
A NN in standby in 2b can run a special service called checkpoint if one
desires.
A Datanode or Checkpointer is not NN mode or even a 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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