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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-9924) [umbrella] Asynchronous HDFS Access
Date Tue, 07 Jun 2016 07:36:21 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9924?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15318054#comment-15318054

Tsz Wo Nicholas Sze commented on HDFS-9924:

> I think AsyncDistributedFileSystem should be annotated as Private, ...

Yes, we should, @Private or @LimitedPrivate.

It seems that there are some serious confusions here.  FileSystem is a user facing public
API, however, DistributedFileSystem is not.  DistributedFileSystem is always an internal API
and never a public API.  Note that FileSystem was annotated as @Public @Stable (in 2010) but
DistributedFileSystem was annotated as @LimitedPrivate @Unstable (in 2012).  Therefore, adding
or changing APIs to DistributedFileSystem do not affect any user facing public API at all.

What have we done so far?  We have added some methods to DistributedFileSystem and a new internal
@Unstable class AsyncDistributedFileSystem.  The FileSystem API remains unchanged.  So there
is no change in any user facing public API at all.

Please let me know if you disagree.  Thanks.

> [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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