Shashikant Banerjee created HDFS-13102:
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             Summary: Implement SnapshotSkipList class to store Multi level 
DirectoryDiffs
                 Key: HDFS-13102
                 URL: https://issues.apache.org/jira/browse/HDFS-13102
             Project: Hadoop HDFS
          Issue Type: Improvement
            Reporter: Shashikant Banerjee
            Assignee: Shashikant Banerjee


HDFS-11225 explains an issue where deletion of older snapshots can take a very 
long time in case the no of snapshot diffs is quite large for directories. For 
any directory under a snapshot, to construct the children list , it needs to 
combine all the diffs from that particular snapshot to the last snapshotDiff 
record and reverseApply to the current children list of the directory on live 
fs. This can take  a significant time if the no of snapshot diffs are quite 
large and changes per diff is significant.

This Jira proposes to store the Directory diffs in a SnapshotSkip list, where 
we store multi level DirectoryDiffs. At each level, the Directory Diff will be 
cumulative diff of k snapshot diffs,

where k is the level of a node in the list. 

 



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