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https://issues.apache.org/jira/browse/HADOOP-15691?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16937719#comment-16937719
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Adam Antal commented on HADOOP-15691:
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Thanks for working on this [~ste...@apache.org]!
> Add PathCapabilities to FS and FC to complement StreamCapabilities
> ------------------------------------------------------------------
>
> Key: HADOOP-15691
> URL: https://issues.apache.org/jira/browse/HADOOP-15691
> Project: Hadoop Common
> Issue Type: New Feature
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Major
> Fix For: 3.3.0
>
> Attachments: HADOOP-15691-001.patch, HADOOP-15691-002.patch,
> HADOOP-15691-003.patch, HADOOP-15691-004.patch
>
>
> This complements the {{StreamCapabilities}} interface by allowing
> applications
> to probe for a specific path on a specific instance of a {{FileSystem}}
> or {{FileContext}} offering a specific feature.
> This is intended to allow applications to determine
> * Whether a method is implemented before calling it and dealing with
> any subsequent UnsupportedOperationException.
> * Whether a specific feature is believed to be available in the remote store.
> As well as a common set of capabilities defined in CommonPathCapabilities,
> file systems are free to add their own capabilities, prefixed with
> fs. + schema + .
>
> The plan is to identify and document more capabilities -and for file systems
> which add new features, for a declaration of the availability of the feature
> to
> always be available.
> The interface may be offered by other classes too; there is no restriction
> here.
> Note
> * The remote store is not expected to be checked for the feature;
> It is more a check of client API and the client's configuration/knowledge
> of the state of the remote system.
> * Permissions are not checked.
> This is needed for
> * HADOOP-14707: declare that a dest FS supports permissions
> * object stores to declare that they offer PUT-in-place alongside
> (slow-rename)
> * Anything else where the implementation semantics of an FS is so different
> caller apps would benefit from probing for the underlying semantics
> I know, we want all filesystem to work *exactly* the same. But it doesn't
> hold, especially for object stores —and to efficiently use them, callers need
> to be able to ask for specific features.
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