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From "Shashikant Banerjee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13102) Implement SnapshotSkipList class to store Multi level DirectoryDiffs
Date Fri, 02 Feb 2018 18:43:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16350793#comment-16350793

Shashikant Banerjee commented on HDFS-13102:

Patch v1 implements a SnapshotSkipList for Directory Diffs. It implements List interface for
DirectoryDiff and provides a linear view of the list through general List API's.

> 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
>            Priority: Major
>         Attachments: HDFS-13102.001.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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