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https://issues.apache.org/jira/browse/HDFS-12975?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16366438#comment-16366438
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Konstantin Shvachko commented on HDFS-12975:
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Hey [~csun], was looking through your patch.
# There are some changes that are not related to incorporating Observer
capabilities into NameNode, like start/stop scripts, {{ReadOnly}} annotations,
{{hdfs-default.xml}}. We should introduce them in separate jira(s). Would be
good to dedicate this mostly the NameNode changes.
# The main question in this regard is whether we define observer role as a
separate class {{ObserverState}} as in your patch or as an attribute (flag) of
the {{StandbyState}}. I see that for example {{startObserverState()}} reuses a
lot of code of {{startStandbyServices()}}. Also in the end ANN should be able
to fail over to either SBN or Observer, so may be we don't need a new state.
Or add it when we really have to.
# White space changes are mostly annoying, but also make it hard to merge /
rebase the branch in the future, which we will have to do a lot.
> Changes to the NameNode to support reads from standby
> -----------------------------------------------------
>
> Key: HDFS-12975
> URL: https://issues.apache.org/jira/browse/HDFS-12975
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Reporter: Konstantin Shvachko
> Assignee: Chao Sun
> Priority: Major
> Attachments: HDFS-12975.000.patch
>
>
> In order to support reads from standby NameNode needs changes to add Observer
> role, turn off checkpointing and such.
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