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From "Xiaobing Zhou (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9924) [umbrella] Asynchronous HDFS Access
Date Wed, 15 Jun 2016 17:51:10 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15332191#comment-15332191
] 

Xiaobing Zhou commented on HDFS-9924:
-------------------------------------

{quote}
With your solution, you will block on request 1 for a long time before resubmit the failed
2-99 request.

This is a inherent defect of lacking the support of callback.
And a better solution is, sorry, but again, using multiple threads
With a thread pool and CompletionService, you can (sometimes) get the failed request first.
{quote}
You just had an extreme example trying to establish cause and effect. If it's really the case,
why not to resort to Future#IsDone() or call Future#get(long timeout, TimeUnit unit) with
neglectable timeout? You don't have to be blocked to send failed requests earlier. 

In addition, the RPC layer is async as is, Connection#receiveRpcResponse is run by a thread
(i.e. Connection extends Thread) to actively buffer the final result into Client#Call as long
as it's available on socket. As a result, The final result is already available in Client#Call
most often. You will not be experiencing the block subject to Future#get unless the result
is not returned by server.

Thank you anyway for the comments.





> [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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