[openstack-dev] [nova] Distributed Database

Andrew Laski andrew at lascii.com
Fri Apr 22 21:32:59 UTC 2016

On Fri, Apr 22, 2016, at 04:27 PM, Ed Leafe wrote:
> OK, so I know that Friday afternoons are usually the worst times to
> write a blog post and start an email discussion, and that the Friday
> immediately before a Summit is the absolute worst, but I did it anyway.
> http://blog.leafe.com/index.php/2016/04/22/distributed_data_nova/
> Summary: we are creating way too much complexity by trying to make Nova
> handle things that are best handled by a distributed database. The
> recent split of the Nova DB into an API database and separate cell
> databases is the glaring example of going down the wrong road.
> Anyway, read it on your flight (or, in my case, drive) to Austin, and
> feel free to pull me aside to explain just how wrong I am. ;-)

I agree with a lot of what Monty wrote in his response. And agree that
given a greenfield there are much better approaches that could be taken
rather than partitioning the database.

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.

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.

I don't want to get too sidetracked on talking about cells. I just
wanted to point out that cells v2 did not come to fruition due to a fear
of distributed databases.

> -- 
> -- Ed Leafe
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