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From "Aaron T. Myers (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2185) HA: HDFS portion of ZK-based FailoverController
Date Mon, 26 Mar 2012 22:36:28 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2185?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13238922#comment-13238922

Aaron T. Myers commented on HDFS-2185:

Patch looks pretty good, Todd. A few small comments:

# Is it intentional that you call "super.setConf(...)" in DFSZKFailoverController#setConf
with the passed-conf as-is, instead of the slightly mutated localNNConf? If it is intentional,
then please move the super.setConf(...) call higher in the method to make that clear.
# Is it necessary for DFSZKFailoverController#getLocalTarget to return a new NNHAServiceTarget
object each time it is called? If so, please add a comment explaining why. If not, then let's
just store a single instance of NNHAServiceTarget instead of the separate conf/nsId/nnId instance
# I think you might end up with a race condition if you don't add a "waitForHAState(1, HAServiceState.STANDBY)"
in TestDFSZKFailoverController#setup after starting the second ZKFCThread.
# A little too much indentation at the end of TestDFSZKFailoverController#setup.
# After the call to "cluster.restartNameNode(0)", I think we should assert that the second
NN is still active. As-written, the test could succeed if the system failed back to the first
NN upon restarting it. This assertion is sort of more a test of the common side of this patch,
though, so feel free to punt.
# "Test-thread which runs a ZK Failover Controller corresponding to a given dummy service"
- it's not a dummy service in this case.
> HA: HDFS portion of ZK-based FailoverController
> -----------------------------------------------
>                 Key: HDFS-2185
>                 URL: https://issues.apache.org/jira/browse/HDFS-2185
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: ha
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Eli Collins
>            Assignee: Todd Lipcon
>         Attachments: Failover_Controller.jpg, hdfs-2185.txt, hdfs-2185.txt, zkfc-design.pdf
> This jira is for a ZK-based FailoverController daemon. The FailoverController is a separate
daemon from the NN that does the following:
> * Initiates leader election (via ZK) when necessary
> * Performs health monitoring (aka failure detection)
> * Performs fail-over (standby to active and active to standby transitions)
> * Heartbeats to ensure the liveness
> It should have the same/similar interface as the Linux HA RM to aid pluggability.

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