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https://issues.apache.org/jira/browse/HDFS-2305?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Aaron T. Myers updated HDFS-2305:
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Attachment: hdfs-2305.1.patch
> Running multiple 2NNs can result in corrupt file system
> -------------------------------------------------------
>
> Key: HDFS-2305
> URL: https://issues.apache.org/jira/browse/HDFS-2305
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: name-node
> Affects Versions: 0.20.2
> Reporter: Aaron T. Myers
> Assignee: Aaron T. Myers
> Attachments: hdfs-2305-test.patch, hdfs-2305.0.patch,
> hdfs-2305.1.patch
>
>
> Here's the scenario:
> * You run the NN and 2NN (2NN A) on the same machine.
> * You don't have the address of the 2NN configured, so it's defaulting to
> 127.0.0.1.
> * There's another 2NN (2NN B) running on a second machine.
> * When a 2NN is done checkpointing, it says "hey NN, I have an updated
> fsimage for you. You can download it from this URL, which includes my IP
> address, which is x"
> And here's the steps that occur to cause this issue:
> # Some edits happen.
> # 2NN A (on the NN machine) does a checkpoint. All is dandy.
> # Some more edits happen.
> # 2NN B (on a different machine) does a checkpoint. It tells the NN "grab the
> newly-merged fsimage file from 127.0.0.1"
> # NN happily grabs the fsimage from 2NN A (the 2NN on the NN machine), which
> is stale.
> # NN renames edits.new file to edits. At this point the in-memory FS state is
> fine, but the on-disk state is missing edits.
> # The next time a 2NN (any 2NN) tries to do a checkpoint, it gets an
> up-to-date edits file, with an outdated fsimage, and tries to apply those
> edits to that fsimage.
> # Kaboom.
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