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

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

     [ https://issues.apache.org/jira/browse/HADOOP-14159?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steve Loughran updated HADOOP-14159:
------------------------------------
    Priority: Minor  (was: Major)

> 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
>            Priority: Minor
>
> 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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