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https://issues.apache.org/jira/browse/HDFS-4808?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13652647#comment-13652647
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Aaron T. Myers commented on HDFS-4808:
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bq. Why cannot this be a general FileSystem functionality? I think this is
general enough. Currently looking at the snapshot related methods added, I do
not see any HDFS specific semantics.
Do you know of any existing or future FileSystem implementations
(LocalFileSystem, S3FileSystem, etc.) which will support snapshots? If they do
ever support snapshots, will they support sub-tree snapshots? (Sub-tree
snapshots is not something I'm aware of any other file system supporting.)
>From what I know of other file systems which support some form of snapshots
>(WAFL, ZFS, etc.), their semantics, conceptual nouns, etc. all differ so
>substantially from one another that I don't think it would be easy (possible?)
>to come up with a single general-purpose snapshot API to cover all of them.
>All other file systems I'm aware of which support snapshots provide their own
>file system-specific APIs for creating, deleting, managing their snapshots.
>This suggests to me that HDFS should expose a file system-specific API as well.
bq. FileSystem currently is both the user API and file system implementors API.
I think file systems that can support snapshots can implement this feature and
file systems that do not can throw unsupported exception.
If literally all other implementers of FileSystem will throw
UnsupportedOperationException, what's the point of putting it in FileSystem at
all?
How about this for a way forward: For now we move the snapshot create/delete
APIs to an HDFS-specific class. If/when another FileSystem implementation shows
up which supports a similar API to the HDFS snapshots API, we can move it to
FileSystem at that point.
> Limit snapshot related methods to DistributedFileSystem
> -------------------------------------------------------
>
> Key: HDFS-4808
> URL: https://issues.apache.org/jira/browse/HDFS-4808
> Project: Hadoop HDFS
> Issue Type: Bug
> Reporter: Suresh Srinivas
>
> HDFS-2802 introduces snapshots related methods into FileSystem. This jira is
> for discussing whether these snapshots related methods are needed in
> FileSystem or should be limited to only DistributedFileSystem.
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