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https://issues.apache.org/jira/browse/HADOOP-9565?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16002879#comment-16002879
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Steve Loughran commented on HADOOP-9565:
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Note how this is a query-only API, allowing for dynamic probes of FS features,
rather than static "does this FS implement a specific interface", and because
its done in the base FSClass, no need to add a new interface to cast an FS to
to look for it. We just need to make the defaults valid for the filesystems,
which we can do by having core-default/xml define the default FS behaviour and
with every FS we manage defining their own.
What about external filesystems? Well, the default resolver looks for a
resource called {{contract/fs-$SCHEMA-features.xml}}. If the people
implementing filesystems copy their contract test XML file into that location
in the production JAR, it will be picked up automatically. This allows the
authors to update their JARs and have the capabilities be visible on Hadoop
implementations with the new API, but still load/run against the old one.
see also: {{StreamCapabilities}}
> Add a Blobstore interface to add to blobstore FileSystems
> ---------------------------------------------------------
>
> Key: HADOOP-9565
> URL: https://issues.apache.org/jira/browse/HADOOP-9565
> Project: Hadoop Common
> Issue Type: Improvement
> Components: fs, fs/s3, fs/swift
> Affects Versions: 2.6.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Attachments: HADOOP-9565-001.patch, HADOOP-9565-002.patch,
> HADOOP-9565-003.patch, HADOOP-9565-004.patch, HADOOP-9565-005.patch,
> HADOOP-9565-006.patch, HADOOP-9565-008.patch, HADOOP-9565-010.patch,
> HADOOP-9565-branch-2-007.patch
>
>
> We can make the fact that some {{FileSystem}} implementations are really
> blobstores, with different atomicity and consistency guarantees, by adding a
> {{Blobstore}} interface to add to them.
> This could also be a place to add a {{Copy(Path,Path)}} method, assuming that
> all blobstores implement at server-side copy operation as a substitute for
> rename.
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