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https://issues.apache.org/jira/browse/HDFS-1489?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12973581#action_12973581
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Ivan Kelly commented on HDFS-1489:
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NNStorage holds the functionality for managing namenode storage directories
which is common to both FSImage and FSEditLog.
FSImage handles loading, saving, upgrading, rollback etc of image files. It
also owns FSEditLog in the latest patch.
The logic behind this whole JIRA is that FSImage & FSEditLog shouldn't be
mutually dependent. The big patch removes the dependency completely. The
NNStorage patch leave the dependency of FSImage on FSEditLog, but works towards
removing the dependency of FSEditLog on FSImage.
> breaking the dependency between FSEditLog and FSImage
> -----------------------------------------------------
>
> Key: HDFS-1489
> URL: https://issues.apache.org/jira/browse/HDFS-1489
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 0.21.0
> Reporter: Diego Marron
> Attachments: HDFS-1489.diff, HDFS-1489.diff, HDFS-1489.pdf,
> NNStorage.diff
>
>
> This is a refactor patch which its main concerns are:
> - breaking the dependency between FSEditLog and FSImage
> - Splitting the abstracting the error handling and directory management,
> - Decoupling Storage from FSImage.
> In order to accomplish the above goal, we will need to introduce new classes:
> - NNStorage: Will care about the storage. It extends Storage class, and will
> contain the StorageDirectories.
> - NNUtils: Some utility static methods on FSImage and FSEditLog will be
> moved here.
> - PersistenceManager: FSNameSystem will now be responsible for managing the
> FSImage & FSEditLog objects. There will be some logic that will have to moved
> out of FSImage to facilite this. For this we propose a PersistanceManager?
> object as follows.
> For more deep details, see the design document uploaded.
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