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From "Justin Joseph (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7455) Introduce HA Service Protocol Interface
Date Wed, 03 Aug 2011 06:51:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7455?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13078606#comment-13078606

Justin Joseph commented on HADOOP-7455:

@Aaron : When an Active Namenode lose the connection to Zookeeper ensemble, it cannot remain
in the Active state. One option is to transition to Standby state, but it is unnecessary,
the same Namenode may be asked to become Active once the connection with Zookeeper is established
again. The second option, the better one, is to move to an idle state - neutral state..

Moving from Active to Standby involves many complexities, at least in Backup Node based HA.
First the Active state needs to be cleaned up; it should transition to Standby; it should
connect to Active Namenode & then trigger a check pointing. This is purely an overhead
considering the fact that the same Namenode may be asked to become Active again soon. 

Neutral state ensures that a Namenode does not act hastily when it loses the connection to
Zookeeper ensemble. Rather it just 'wait & watch'.

> 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
>         Attachments: HADOOP-7455.1.patch, HADOOP-7455.2.patch, HADOOP-7455.3.patch, HADOOP-7455.4.patch,
> This jira introduces a protocol interface to be implemented by services that provide
HA functionality.

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