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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2627) HA: determine DN's view of which NN is active based on heartbeat responses
Date Mon, 05 Dec 2011 21:26:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2627?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13163049#comment-13163049
] 

Todd Lipcon commented on HDFS-2627:
-----------------------------------

The only non-test use case for {{isAlive}} seems to be from {{BlockPoolSliceScanner}} and
{{DataBlockScanner}}, where they're really trying to figure out whether they should stop scanning
the block pool. If the BPOS is connected to any NN at all (regardless of active/standby) it
needs to report {{true}} so that the scanners don't stop running.

It would be nice to clean up these calls and specify in their function name that they're only
meant for use in tests, but it seems out-of-scope for this JIRA.
                
> HA: determine DN's view of which NN is active based on heartbeat responses
> --------------------------------------------------------------------------
>
>                 Key: HDFS-2627
>                 URL: https://issues.apache.org/jira/browse/HDFS-2627
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: data-node, ha, name-node
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2627-v1.txt
>
>
> This is the first part of the design described in [this comment|https://issues.apache.org/jira/browse/HDFS-1972?focusedCommentId=13160601&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13160601]
in HDFS-1972. When the DNs start, they should not consider either of the NNs in a block pool
to be the active one. Rather, the NNs should include their HA state as part of the heartbeat
response to the DN, and the DN will believe whichever NN claims to be active at a higher transaction
ID.

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