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HDFS, mail # dev - Backwards compatibility of FileSystem interface.


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Re: Backwards compatibility of FileSystem interface.
Steve Loughran 2013-05-31, 20:49
(forwarding to common-dev which is where this discussion about APIs should
go)
   1. FileSystem API may add new methods from version to version. There's
   some list operation that's gone in too.
   2. I don't think there are any guarantees that we don't add new methods
   to a base class -it's why they are often preferred to an interface.
   3. You are free to add the new methods into your implementation -just
   don't mark them as @Override and they will compile, and should be picked up
   in the later version

This adds an extra point to the compatibility JIRA: plugins.

"classes that subclass a Hadoop class to provide a plugin point should
expect to need recompiling on each major version, possibly with the
handling of changes to methods. There is no guarantee that a plugin built
for an earlier version of Hadoop can be directly used in the later version,
and implementors of plugins should expect to have to release new versions"

On 31 May 2013 14:58, Jay Vyas <[EMAIL PROTECTED]> wrote:

> For context - It appears that over time the FileSystem has changed the
> signature to the "createNonRecursive" method, (in 2.x there are 3
> signatures, in 1.x, there are 2 signatures).
>
> [root@jvyas hadoop-common]# git checkout branch-1.1
> Switched to branch 'branch-1.1'
> [root@jvyas hadoop-common]# grep NonRec
> ./src/core/org/apache/hadoop/fs/FileSystem.java
>   public FSDataOutputStream createNonRecursive(Path f,
>     return this.createNonRecursive(f, FsPermission.getDefault(),
>   public FSDataOutputStream createNonRecursive(Path f, FsPermission
> permission,
>     throw new IOException("createNonRecursive unsupported for this
> filesystem "
>
> [root@jvyas hadoop-common]# git checkout branch-2.1.0-alpha
> Switched to branch 'branch-2.1.0-alpha'
>
> [root@jvyas hadoop-common]# cat
>
> ./hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileSystem.java
> | grep NonRec
> | grep NonRec
>
> public FSDataOutputStream createNonRecursive(Path f,
>     return this.createNonRecursive(f, FsPermission.getDefault(),
> public FSDataOutputStream createNonRecursive(Path f, FsPermission
> permission,
>      return createNonRecursive(f, permission,
> public FSDataOutputStream createNonRecursive(Path f, FsPermission
> permission,
>       throw new IOException("createNonRecursive unsupported for this
> filesystem
>
>
> So, this (im assuming) is to retain backwards compatibility.  But it when
> new API calls are made older FileSystem implementations dont work anymore.
>
> For context, here is a closely related JIRA
>
>
> https://issues.apache.org/jira/browse/HADOOP-6886?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
>
>
> On Fri, May 31, 2013 at 6:09 AM, Steve Loughran <[EMAIL PROTECTED]
> >wrote:
>
> > Jay, this is is more a common-dev question, as it goes beyond hdfs
> >
> > On 31 May 2013 02:07, Jay Vyas <[EMAIL PROTECTED]> wrote:
> >
> > > Hi :
> > >
> > > Are FileSystem interfaces gauranteed to retain semantics of the old
> > > FileSystem contract?
> > >
> >
> > retain the explicit semantics, yes. Implementations may change some
> > implementation details which may becomes visible
> >
> >
> > >
> > > Im noticing that the new FileSystem uses the "CreateFlag" class, which
> > > older ones did not, and I'm wondering wether the deprecation of some
> > > FileSystem methods (i.e. createNonRecursive) will eventually be
> entirely
> > > phased out.
> > >
> > > This is in reference to some issues with HBASE and the
> createNonRecursive
> > > implementation which varies across different hadoop versions.
> > >
> > >
> > can you point to the JIRAs? I presume they are append related?
> >
> >
> > > --
> > > Jay Vyas
> > > http://jayunit100.blogspot.com
> > >
> >
>
>
>
> --
> Jay Vyas
> http://jayunit100.blogspot.com
>