[
https://issues.apache.org/jira/browse/HDFS-2802?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13490960#comment-13490960
]
Aaron T. Myers commented on HDFS-2802:
--------------------------------------
bq. Eli, the memory usage in ATM's proposal is not O(1) since it adds tags for
every INode, therefore, it is O(N), where N is the number of INodes...
I believe the distinction here is how much memory is used _at snapshot creation
time_. Both of the current proposals are constant in terms of time/space at
snapshot creation time, but you're right that the most recent proposal I posted
would add some overhead per INode.
In any case, I agree that the solution described in the most recent document
posted by Suresh will be more space efficient than the latest proposal I
posted. No disagreement there. This is what I was referring to when I said
"This [the design posted by Suresh] has the advantage of saving NN memory space
for files/directories which have never had snapshots created of them."
> Support for RW/RO snapshots in HDFS
> -----------------------------------
>
> Key: HDFS-2802
> URL: https://issues.apache.org/jira/browse/HDFS-2802
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: data-node, name-node
> Reporter: Hari Mankude
> Assignee: Hari Mankude
> Attachments: HDFS-2802.20121101.patch,
> HDFS-2802-meeting-minutes-121101.txt, HDFSSnapshotsDesign.pdf, snap.patch,
> snapshot-design.pdf, snapshot-design.tex, snapshot-one-pager.pdf,
> Snapshots20121018.pdf, Snapshots20121030.pdf
>
>
> Snapshots are point in time images of parts of the filesystem or the entire
> filesystem. Snapshots can be a read-only or a read-write point in time copy
> of the filesystem. There are several use cases for snapshots in HDFS. I will
> post a detailed write-up soon with with more information.
--
This message is automatically generated by JIRA.
If you think it was sent incorrectly, please contact your JIRA administrators
For more information on JIRA, see: http://www.atlassian.com/software/jira
