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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1974) HA: Introduce active and standby states to the namenode
Date Tue, 09 Aug 2011 21:50:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13081951#comment-13081951

Aaron T. Myers commented on HDFS-1974:

Thanks a lot for addressing my concerns, Suresh. The latest patch looks a lot better to me.

bq. My concern with the common change is adding a notion of StandbyException to IPC. We could
have a separate discussion about whether the notion of StandbyException belongs to IPC layer
or to the service. One thing I have been thinking is for upper layers to install error/exception
handlers. That upper layers could use exception handler to handle StandbyException.

My point isn't that StandbyException is necessarily the right approach, just that I do think
the IPC layer should be responsible for the mechanics of client failover, and thus that there
should be some way for an exception thrown by a remote service to indicate to the client that
a request should be retried against another server. But, this discussion should probably happen
on a separate JIRA.

bq. I also think that having a method to transition to every state, means too many methods
in HAState. So I have changed the patch to use setState() and setStateInternal(). See if it
makes more sense now.

I agree. The latest patch looks much better to me in this regard.

Two final comments. +1 once these are addressed:

# The two-argument constructor in {{UnsupportedActionException}} doesn't actually use the
{{action}} parameter.
# I don't think {{listCorruptFileBlocks}} is a write operation.

> HA: Introduce active and standby states to the namenode
> -------------------------------------------------------
>                 Key: HDFS-1974
>                 URL: https://issues.apache.org/jira/browse/HDFS-1974
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: name-node
>            Reporter: Suresh Srinivas
>            Assignee: Suresh Srinivas
>         Attachments: HDFS-1974.1.patch, HDFS-1974.2.patch, HDFS-1974.3.patch, HDFS-1974.4.patch,
HDFS-1974.5.patch, HDFS-1974.patch
> Currently namenode supports active, secondary and backup roles. To support namenode high
availability, active and standby states are needed. Note that this is different from the existing
notion of namenode role, where a namenode cannot transition from one role to the other.

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