Steve Loughran created HADOOP-12614:
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Summary: Add a generic .isOffline() method to filesystems to probe
availability
Key: HADOOP-12614
URL: https://issues.apache.org/jira/browse/HADOOP-12614
Project: Hadoop Common
Issue Type: Improvement
Components: fs
Affects Versions: 2.7.1
Reporter: Steve Loughran
Priority: Minor
Looking at some of the spark `HistoryServer` code, they do reflection games to
check whether HDFS is in safe mode or not, games which vary with version and
could be at risk of failing with the client/server split (fortunately, it's all
client-side). Nor do the checks apply to other filesystems, which could have
their own online/offline state.
I propose adding the new methods {{FileSystem.isOffline()}},
{{FileContext.isOffline()}}, to return true if an FS knows that it is offline.
For HDFS: Safe mode. For other filesystems? Maybe network state, disk being
r/W, etc. Their choice. The default would be false: an FS is not offline,
obvously, {{!isOffline()}} doesn't guarantee the FS is fully functional; that's
why I propose {{isOffline()}}; less dangerous than the opposite values of
{{isLive()}} or {{isAvailable()}}, which may be making promises which cannot
hold
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