[jira] [Created] (HADOOP-14159) Add some Java-8 friendly way to work with RemoteIterable, especially listings

["Steve Loughran (JIRA)" <ji...@apache.org>]

Steve Loughran created HADOOP-14159:
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             Summary: Add some Java-8 friendly way to work with RemoteIterable, especially listings
                 Key: HADOOP-14159
                 URL: https://issues.apache.org/jira/browse/HADOOP-14159
             Project: Hadoop Common
          Issue Type: Improvement
          Components: fs
    Affects Versions: 3.0.0-alpha2
            Reporter: Steve Loughran


There's a fair amount of Hadoop code which uses {{FileSystem.listStatus(path) }} just to get an {{FileStatus[]}} array which they can then iterate over in a {{for}} loop.

This is inefficient and scales badly, as the entire listing is done before the compute; it cannot handle directories with millions of entries. 

The listLocatedStatus() calls return a RemoteIterator class, which can't be used in for loops as it has the right to throw an IOE in any hasNext/next call. That doesn't matter, as we now have closures and simple stream operations.

{code}
 listLocatedStatus(path).filter((st) -> st.length > 0).apply(st -> fs.delete(st.path))}}
{code}

See? We could do shiny new closure things. It wouldn't necessarily need changes to FileSystem either, just something which took {{RemoteIterator}} and let you chain some closures off it, similar to the java 8 streams operations.

Once implemented, we can move to using it in the Hadoop code wherever we  use listFiles() today



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