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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-13172) And an UnsupportedFeatureException for Filesystems to throw on unsupported operations
Date Wed, 18 May 2016 19:31:13 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-13172?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15289646#comment-15289646

Steve Loughran commented on HADOOP-13172:

Right. In HADOOP-13130 I Was throwing {{UnsupportedOperationException}}; Chris flagged up
that that would have been a different error than an IOE, which things often expect to catch,
and which all the current impls throw. I'd forgotten about HADOOP-12726, though I had picked
up the same pattern

# we should have an explicit way to distinguish unsupported-ness from any other IOE.
# In HADOOP-12726, [~templedf] has a patch to move all of the IOEs to {{UnsupportedOperationException}}

I think it comes down to: what do callers expect the method to throw if its not there. Most
seem to be throwing generic IOEs, which is fundamentally not that useful in distinguishing
"unimplemented" to "not there".

Maybe lets return to that discussion, as it would be where the fs spec would need clarification

> And an UnsupportedFeatureException for Filesystems to throw on unsupported operations
> -------------------------------------------------------------------------------------
>                 Key: HADOOP-13172
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13172
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: fs
>    Affects Versions: 2.8.0
>            Reporter: Steve Loughran
>            Priority: Minor
> Filesystems which don't support things like append() tend to throw a simple IOE, which
makes it hard to distinguish "append didn't work for some IO problem" and "append isn't implemented".
> If we add a new exception, {{UnsupportedFeatureException}}, make it the strict failure
mode of such operations if not supported and patch all our filesystems to raise it, then at
least code has a straightforward check. Same for any other unimplemented feature

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