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From Gary Helmling <ghelml...@gmail.com>
Subject Re: [DISCUSS] No regions on Master node in 2.0
Date Tue, 12 Apr 2016 18:55:43 GMT
>
> # Without meta on master, we double assign and lose data.
>
> I doubt meta on master solve this problem.
> This has more to do on the fact that balancer, assignment, split, merge
> are disjoint operations that are not aware of each other.
> also those operation in general consist of multiple steps and if the master
> crashes you may end up in an inconsistent state.
>
>
Meta-on-master does dramatically improve things.  For example, it makes it
possible to cold-start HBase under load, where a non-meta-serving master is
never able to successfully complete initialization.  This is the difference
between a cluster being able to come to a healthy state vs. one that is
never able to complete assignments, communicate those assignments to
clients and come to a steady state.


> this is what proc-v2 should solve. since we are aware of each operation
> there is no chance of double assignment and similar by design.
>
>
Again, I think it is difficult to compare an existing feature that is
working in production use vs. one that is actively being developed in
master.

Preventing double assignment sounds great.  When happens when the update of
meta to communicate this to clients fails?  So long as meta is served
elsewhere you still have distributed state.

Until we have an alternative that is feature complete and has demonstrated
success and stability in production use, I don't see how we can even
propose removing a feature that is solving real problems.

I also think that this proposed direction will amplify our release problems
and get us further away from regular, incremental releases.  Master will
remain unreleaseable indefinitely until proc v2 development is finished,
and even initial releases will have problems that need to be ironed out.
Ironing out issues in initial releases is not unexpected, but by removing
existing solution we would be forcing a big-bang approach where everything
has to work before anyone can move over to 2.0, which increases pressure
for users to stay on 1.x releases, which increases pressure to backport
features and brings us closer to the Hadoop way.  I would much rather see
us working on incrementally improving what we have and proving out new
solutions piece by piece.

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