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https://issues.apache.org/jira/browse/HDFS-4103?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13485771#comment-13485771
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Tsz Wo (Nicholas), SZE commented on HDFS-4103:
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There is a well-known data structure supportting
- O(1) snapshot creation,
- O(1) access slowdown, and
- O(1) modification space and time.
See http://www.cs.cmu.edu/~sleator/papers/Persistence.htm
The data structure collides with the ideas Suresh, Jing and I were discussing.
We probably will use it in our implementation.
> 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: name-node
> Reporter: Tsz Wo (Nicholas), SZE
> Assignee: Tsz Wo (Nicholas), SZE
>
> 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.
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