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https://issues.apache.org/jira/browse/HDFS-3862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13443518#comment-13443518
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Todd Lipcon commented on HDFS-3862:
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I think this might be the case for BookKeeper as well. Any of the folks working
on BKJM want to take this on? I anticipate we would add a simple API to
JournalManager like: {{boolean isNativelySingleWriter();}} or {{boolean
needsExternalFencing();}}. Then the failover code could check the shared
storage dir to see if this is the case, and if so, not error out if the user
doesn't specify a fence method.
> QJM: don't require a fencer to be configured if shared storage has built-in
> single-writer semantics
> ---------------------------------------------------------------------------------------------------
>
> Key: HDFS-3862
> URL: https://issues.apache.org/jira/browse/HDFS-3862
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: ha
> Affects Versions: QuorumJournalManager (HDFS-3077)
> Reporter: Todd Lipcon
>
> Currently, NN HA requires that the administrator configure a fencing method
> to ensure that only a single NameNode may write to the shared storage at a
> time. Some shared edits storage implementations (like QJM) inherently enforce
> single-writer semantics at the storage level, and thus the user should not be
> forced to specify one.
> We should extend the JournalManager interface so that the HA code can operate
> without a configured fencer if the JM has such built-in fencing.
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