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From Dhruba Borthakur <dhr...@gmail.com>
Subject Re: Merging Namenode Federation feature (HDFS-1052) to trunk
Date Mon, 14 Mar 2011 17:43:07 GMT
Hi folks,

The design for the federation work has been a published and there is a very
well-written design document. It explains the pros-and-cons of each design
point. It would be nice if more people can review this document and provide
comments on how to make it better. The implementation is in progress but
that does not mean that the

Allen: can you pl describe what you mean by  "It sounds like merging into
trunk is extremely premature". If we can make all unit tests pass
successfully on the branch, then do you think we should merge that branch
into the trunk?

Konstantin: I agree that federation introduces new code complexity. But it
is a fact that introducing a new heavy-weight feature will add complexity.
If you have a different proposal (and implementation) to scale namenode,
please share it with us and we can then evaluate these designs in terms on
complexity/feature. If you have questions about certain issues in the
design, it would be great if you can ask them now. Hopefully, the folks
doing the implementation can then provide you performance numbers to
alleviate your concerns.

>From that way I look at it, I think the federation-feature is a huge
positive step in the right direction.


On Mon, Mar 14, 2011 at 10:28 AM, Konstantin Shvachko

> Allen is right.
> This is a huge new feature with 86 jiras already filed, which substantially
> increases the complexity of the code base.
> Having an in-depth motivation and benchmarking will be needed before the
> community decides on adopting it for support.
> Thanks,
> --Konstantin
> On Sat, Mar 12, 2011 at 8:43 AM, Allen Wittenauer
> <awittenauer@linkedin.com>wrote:
> >
> > On Mar 3, 2011, at 2:41 PM, Suresh Srinivas wrote:
> >
> > > We have started pushing changes for namenode federation in to the
> feature
> > branch HDFS-1052. The work items are created as subtask of the jira
> > HDFS-1052 and are based on the design document published in the same
> jira.
> > By the end of this week, we will complete pushing the changes to
> HDFS-1052
> > branch. Though the changes in these jiras are already committed, please
> do
> > provide your feedback on either HDFS-1052 or its subtasks. New items that
> > come out of the feedback will be addressed in new jiras.
> >
> > >
> > > Current status of the development:
> > > # The testing of this feature is underway. Most of the basic
> > functionality has been tested both for a single namenode cluster (for
> > backward compatibility) and with multiple namenodes.
> > > # All the existing tests and newly added tests pass (same as trunk).
> > >
> > > We plan on merging this branch to trunk after a week or two. This will
> > help us continue make future changes on the trunk. I will send an
> > announcement before merging the federation branch into trunk.
> > >
> >
> >        It sounds like merging into trunk is extremely premature.  That
> > said, I'm still trying to understand the why's around this.
> >
> >        To me, this series of changes looks like it is going to make
> running
> > a grid much much harder for very little benefit.  In particular, I don't
> see
> > the difference between running multiple NN/DN combinations verses running
> > federation, especially with client side mount tables in play.
> >
> >

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