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https://issues.apache.org/jira/browse/HADOOP-7455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13108231#comment-13108231
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Suresh Srinivas commented on HADOOP-7455:
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Sorry, I missed these comments earlier.
The reason why I do not have start*() methods is, this is an interface
implemented by a server. Without a server being available there is no one to
field these requests. The way existing interface will fit in with HA framework
is:
start, stop scripts called by HA framework will call existing start and stop
scripts.
For the rest, such as monitoring, making a server active/standby, this
interface will be invoked and will affect it by talking to a server.
bq. Neutral state is the protocol which ensures that only one Active Namenode
will be present at a time. The approach says 'Avoid the possibility of having
two Active Namenodes; rather than do fencing later to prevent the
inconsistencies that can be caused by two Active Namenodes'. This is the key to
understand the intent behind neutral state.
I have not seen this kind of state in HA frameworks. I do not think there is a
reliable way other than fencing to handle partitions.
bq. Once the Namenode (active / standby) loses the connection to Zookeeper, it
will relinquish it's current role & stays idle by transitioning to neutral
state. Once the Zookeeper service is available again to the Namenode, it
conducts the active instance election once again. Based on the result of the
election it decides the new role.
Why should it go to neutral state. Why not standby?
> Introduce HA Service Protocol Interface
> ---------------------------------------
>
> Key: HADOOP-7455
> URL: https://issues.apache.org/jira/browse/HADOOP-7455
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: util
> Reporter: Suresh Srinivas
> Assignee: Suresh Srinivas
> Fix For: HA Branch (HDFS-1623)
>
> Attachments: HADOOP-7455.1.patch, HADOOP-7455.2.patch,
> HADOOP-7455.3.patch, HADOOP-7455.4.patch, HADOOP-7455.5.patch, HDFS-7454.patch
>
>
> This jira introduces a protocol interface to be implemented by services that
> provide HA functionality.
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