[openstack-dev] [Nova] Does Nova really need an SQL database?

Joe Gordon joe.gordon0 at gmail.com
Mon Nov 18 23:32:26 UTC 2013

On Mon, Nov 18, 2013 at 4:08 PM, yunhong jiang <
yunhong.jiang at linux.intel.com> wrote:

> On Mon, 2013-11-18 at 14:09 -0800, Joe Gordon wrote:
> >
> > Phil Day discussed this at the summit and I have finally gotten around
> > to posting a POC of this.
> >
> > https://review.openstack.org/#/c/57053/
> Hi, Joe, why you think the DB is not exact state in your followed commit
> message? I think the DB is updated to date by resource tracker, am I
> right (the resource tracker get the underlying resource information
> periodically but I think that information is mostly static). And I think
> the scheduler retry mainly comes from the race condition of multiple
> scheduler instance.

You answered the question yourself, the compute nodes (indirectly) update
the DB periodically, so the further you are from the last periodic update
the less up to date the DB is.

Its there for both reasons.  But yes it was originally put there because of
the multi scheduler race condition.

> "We already have the concept that the DB isn't the exact state of the
> world, right now it's updated every 10 seconds. And we use the scheduler
> retry mechanism to handle cases where the scheduler was wrong. "
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