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https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15316494#comment-15316494
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Allen Wittenauer commented on HDFS-9924:
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bq. We did not need a branch here since, as mentioned before, this change was 
adding mostly new code but not changing existing code much. Therefore, this 
feature won't hurt stability.

It's a new feature with a significantly large API surface area. It should 
absolutely require extra scrutiny before going in, new code or not.

bq. You might be upset by other features such as HDFS symlink.

I was actually thinking of some of the crazy things that are going on in YARN. 

bq.  I believe the PMC is already closely watching the commits.

... and you'd be very wrong.  Some of the things getting added with no 
resistance is just amazing to me.  (e.g., "let's destroy the NN box by writing 
metrics to a log outside the metrics system using config parameters that don't 
match anything else in HDFS" is my current favorite.)

> [umbrella] Asynchronous HDFS Access
> -----------------------------------
>
>                 Key: HDFS-9924
>                 URL: https://issues.apache.org/jira/browse/HDFS-9924
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: fs
>            Reporter: Tsz Wo Nicholas Sze
>            Assignee: Xiaobing Zhou
>         Attachments: AsyncHdfs20160510.pdf
>
>
> This is an umbrella JIRA for supporting Asynchronous HDFS Access.
> Currently, all the API methods are blocking calls -- the caller is blocked 
> until the method returns.  It is very slow if a client makes a large number 
> of independent calls in a single thread since each call has to wait until the 
> previous call is finished.  It is inefficient if a client needs to create a 
> large number of threads to invoke the calls.
> We propose adding a new API to support asynchronous calls, i.e. the caller is 
> not blocked.  The methods in the new API immediately return a Java Future 
> object.  The return value can be obtained by the usual Future.get() method.



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