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https://issues.apache.org/jira/browse/HDFS-13102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16372323#comment-16372323
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Tsz Wo Nicholas Sze commented on HDFS-13102:
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Hi [~shashikant], I believe your idea on adding diffSetIndexList might work but
the problem is that it needs extra memory. What are the advantages of having
diffSetIndexList?
If we search "skip list implementation" around, we may find quite a few
implementations. I could not see any implementations have some like
diffSetIndexList.
> For example, let's say we have a skip interval of 5 with total of 125
> snapshots. ...
BTW, I cannot understand your example since the figures are not shown correctly.
> 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-13102.002.patch,
> HDFS-13102.003.patch, HDFS-13102.004.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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