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https://issues.apache.org/jira/browse/HDFS-2681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13187186#comment-13187186
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Bikas Saha commented on HDFS-2681:
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About the GC pause scenario (and others like it). Lets not mix up election with
operation safety. What this library provides is a signal about whether one is a
leader or not. By itself, that does not solve the problems of whether that
signal was properly processed or not. E.g. a potential solution to the GC pause
(or any NN hung case) would be to not have the NN participate in leader
election directly. A failover controller (whose design ensures 0 or cheap GC
pauses) could handle the leader election and terminate hung NN's when its are
no longer a master.
Let me address some of the comments in a subsequent patch. I need to learn a
little more Java before I can do it to my liking.
> Add ZK client for leader election
> ---------------------------------
>
> Key: HDFS-2681
> URL: https://issues.apache.org/jira/browse/HDFS-2681
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ha
> Affects Versions: HA branch (HDFS-1623)
> Reporter: Suresh Srinivas
> Assignee: Bikas Saha
> Fix For: HA branch (HDFS-1623)
>
> Attachments: HDFS-2681.HDFS-1623.patch, HDFS-2681.HDFS-1623.patch,
> HDFS-2681.HDFS-1623.patch, HDFS-2681.HDFS-1623.patch, Zookeeper based Leader
> Election and Monitoring Library.pdf
>
>
> ZKClient needs to support the following capabilities:
> # Ability to create a znode for co-ordinating leader election.
> # Ability to monitor and receive call backs when active znode status changes.
> # Ability to get information about the active node.
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