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https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13537255#comment-13537255
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Suresh Srinivas commented on HDFS-4103:
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[~atm] Thank you for offering to review. As Nicholas pointed out, this is the
core change, and more reviews would be good. However, it would be good to wrap
this up soon. Waiting for a day or two should be okay. But in case your holiday
plans come in the way, please post a comment. We could always have subsequent
jiras to address the review comments. The reason for trying to get this change
in soon is, the next set of jiras are all blocked on this core functionality.
Committing this would unblock those jiras.
> Support O(1) snapshot creation
> ------------------------------
>
> Key: HDFS-4103
> URL: https://issues.apache.org/jira/browse/HDFS-4103
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: namenode
> Affects Versions: Snapshot (HDFS-2802)
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
> Attachments: h4103_20121129.patch, h4103_20121202b.patch,
> h4103_20121202.patch, h4103_20121209b.patch, h4103_20121209.patch,
> h4103_20121210b.patch, h4103_20121210.patch, h4103_20121211.patch,
> h4103_20121212b.patch, h4103_20121212.patch, h4103_20121213.patch,
> h4103_20121215b.patch, h4103_20121215.patch, h4103_20121216.patch,
> h4103_20121217b.patch, h4103_20121217.patch, h4103_20121218.patch,
> h4103_20121219.patch
>
>
> In our first snapshot implementation, snapshot creation runs in O(N) and
> occupies O(N) memory space, where N = # files + # directories + # symlinks in
> the snapshot. The advantages of the implementation are that there is no
> additional cost for the modifications after snapshots are created, and it
> leads to a simple implementation.
> In this JIRA, we optimize snapshot creation to O(1) although it introduces
> additional cost in the modifications after snapshots are created. Note that
> the INode is given as an assumption, otherwise, there is a non-constant cost
> to find the INode.
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