[jira] [Created] (HDFS-4103) Support O(1) snapshot creation

["Tsz Wo (Nicholas), SZE (JIRA)" <ji...@apache.org>]

Tsz Wo (Nicholas), SZE created HDFS-4103:
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             Summary: 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


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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