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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13102) Implement SnapshotSkipList class to store Multi level DirectoryDiffs
Date Tue, 27 Feb 2018 22:34:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16379404#comment-16379404

Tsz Wo Nicholas Sze commented on HDFS-13102:

- In addFirst and addLast, pass nodeLevel to new SkipListNode and remove the second SkipListNode
- Remove the skipTo parameter from the SkipDiff constructor since it is always null.

> 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
>          Components: snapshots
>            Reporter: Shashikant Banerjee
>            Assignee: Shashikant Banerjee
>            Priority: Major
>         Attachments: HDFS-13102.001.patch, HDFS-13102.002.patch, HDFS-13102.003.patch,
HDFS-13102.004.patch, HDFS-13102.005.patch, HDFS-13102.006.patch, HDFS-13102.007.patch
> 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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