[openstack-dev] [nova] Distributed Database

Morgan Fainberg morgan.fainberg at gmail.com
Fri Apr 22 22:17:42 UTC 2016

On Fri, Apr 22, 2016 at 2:57 PM, Dan Smith <dms at danplanet.com> wrote:

> > However I do want to point out that cells v2 is not just about dealing
> > with scale in the database. The message queue is another consideration,
> > and as far as I know there is not an analog to the "distributed
> > database" option available for the persistence layer.
> Yeah, it's actually *mostly* about the messaging layer. In fact, if you
> don't want to fragment the database, I'm not sure you have to. Thinking
> with my Friday brain, I don't actually think it would be a problem if
> you configured all the cells (including the cemetery cell) to use the
> same actual database, but different queues. Similarly, you should be
> able to merge and split cells pretty easily if it's convenient for
> whatever reason.
This would be a very interesting direction to explore. Focus on the pain
points of the message queue and then look at addressing the beast that is
the database layer separately. I am going to toss support in behind a lot
of what has been said in this thread already. But I really wanted to voice
my support for exploring this option if/when we have a bit of time. Not
fragmenting the DB unless it's really needed, is a good approach.

With that all said... I wouldn't want to derail work simply because of a
"nice to have" option.

> > Additionally with v1 we found that deployers have enjoyed being able to
> > group their hardware with cells. Baremetal goes in this cell, SSD filled
> > computes over here, and spinning disks over there. And beyond that
> > there's the ability to create a cell, fill it with hardware, and then
> > test it without plugging it up to the production API. Cells provides an
> > entry point for poking at things that isn't available without it.
> People ask me about this all the time. I think it's a bit of a false
> impression of what it's for, but the ability to stand up a chunk of new
> functionality with a temporary API and then merge it into the larger
> deployment is something people seem to like.
> --Dan
Interesting. I never considered cells to work like a POC environment.

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