Steve Loughran commented on MAPREDUCE-5907:

Catching up on this after spending many weeks in HADOOP-13786

* Performance boosts with s3 are moot because both the v1 and v2 algorithms are 
unreliable with raw s3, and slow even with a consistency layer; it's obsolete.
* none of the other stores *currently* do anything with the listFiles

accordingly, we don't see any immediate benefit in moving to the API, But 
if/when someone does implement the listFiles call in a store which also offers 
consistent metadata and O(1) renames, then this will help, especially in v1, 
where the listing is done in the serialized phase of job commit

> Improve getSplits() performance for fs implementations that can utilize 
> performance gains from recursive listing
> ----------------------------------------------------------------------------------------------------------------
>                 Key: MAPREDUCE-5907
>                 URL: https://issues.apache.org/jira/browse/MAPREDUCE-5907
>             Project: Hadoop Map/Reduce
>          Issue Type: Improvement
>          Components: client
>    Affects Versions: 2.4.0
>            Reporter: Sumit Kumar
>            Assignee: Sumit Kumar
>            Priority: Major
>              Labels: BB2015-05-TBR
>         Attachments: MAPREDUCE-5907-2.patch, MAPREDUCE-5907-3.patch, 
> MAPREDUCE-5907.patch
> FileInputFormat (both mapreduce and mapred implementations) use recursive 
> listing while calculating splits. They however do this by doing listing level 
> by level. That means to discover files in /foo/bar means they do listing at 
> /foo/bar first to get the immediate children, then make the same call on all 
> immediate children for /foo/bar to discover their immediate children and so 
> on. This doesn't scale well for object store based fs implementations like s3 
> and swift because every listStatus call ends up being a webservice call to 
> backend. In cases where large number of files are considered for input, this 
> makes getSplits() call slow. 
> This patch adds a new set of recursive list apis that gives opportunity to 
> the fs implementations to optimize. The behavior remains the same for other 
> implementations (that is a default implementation is provided for other fs so 
> they don't have to implement anything new). However for objectstore based fs 
> implementations it provides a simple change to include recursive flag as true 
> (as shown in the patch) to improve listing performance.

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