Looks like it's a complicated problem, and nova-scheduler can't scale-out
horizontally in active/active mode.

Maybe we should illustrate the problem in the HA docs.

http://docs.openstack.org/high-availability-guide/content/_schedulers.html

Thanks for everybody's attention.

2015-03-05 5:38 GMT+08:00 Mike Bayer <mba...@redhat.com>:

>
>
> Attila Fazekas <afaze...@redhat.com> wrote:
>
> > Hi,
> >
> > I wonder what is the planned future of the scheduling.
> >
> > The scheduler does a lot of high field number query,
> > which is CPU expensive when you are using sqlalchemy-orm.
> > Does anyone tried to switch those operations to sqlalchemy-core ?
>
> An upcoming feature in SQLAlchemy 1.0 will remove the vast majority of CPU
> overhead from the query side of SQLAlchemy ORM by caching all the work done
> up until the SQL is emitted, including all the function overhead of
> building
> up the Query object, producing a core select() object internally from the
> Query, working out a large part of the object fetch strategies, and finally
> the string compilation of the select() into a string as well as organizing
> the typing information for result columns. With a query that is constructed
> using the “Baked” feature, all of these steps are cached in memory and held
> persistently; the same query can then be re-used at which point all of
> these
> steps are skipped. The system produces the cache key based on the in-place
> construction of the Query using lambdas so no major changes to code
> structure are needed; just the way the Query modifications are performed
> needs to be preceded with “lambda q:”, essentially.
>
> With this approach, the traditional session.query(Model) approach can go
> from start to SQL being emitted with an order of magnitude less function
> calls. On the fetch side, fetching individual columns instead of full
> entities has always been an option with ORM and is about the same speed as
> a
> Core fetch of rows. So using ORM with minimal changes to existing ORM code
> you can get performance even better than you’d get using Core directly,
> since caching of the string compilation is also added.
>
> On the persist side, the new bulk insert / update features provide a bridge
> from ORM-mapped objects to bulk inserts/updates without any unit of work
> sorting going on. ORM mapped objects are still more expensive to use in
> that
> instantiation and state change is still more expensive, but bulk
> insert/update accepts dictionaries as well, which again is competitive with
> a straight Core insert.
>
> Both of these features are completed in the master branch, the “baked
> query”
> feature just needs documentation, and I’m basically two or three tickets
> away from beta releases of 1.0. The “Baked” feature itself lives as an
> extension and if we really wanted, I could backport it into oslo.db as well
> so that it works against 0.9.
>
> So I’d ask that folks please hold off on any kind of migration from ORM to
> Core for performance reasons. I’ve spent the past several months adding
> features directly to SQLAlchemy that allow an ORM-based app to have routes
> to operations that perform just as fast as that of Core without a rewrite
> of
> code.
>
> > The scheduler does lot of thing in the application, like filtering
> > what can be done on the DB level more efficiently. Why it is not done
> > on the DB side ?
> >
> > There are use cases when the scheduler would need to know even more data,
> > Is there a plan for keeping `everything` in all schedulers process
> memory up-to-date ?
> > (Maybe zookeeper)
> >
> > The opposite way would be to move most operation into the DB side,
> > since the DB already knows everything.
> > (stored procedures ?)
> >
> > Best Regards,
> > Attila
> >
> >
> > ----- Original Message -----
> >> From: "Rui Chen" <chenrui.m...@gmail.com>
> >> To: "OpenStack Development Mailing List (not for usage questions)" <
> openstack-dev@lists.openstack.org>
> >> Sent: Wednesday, March 4, 2015 4:51:07 AM
> >> Subject: [openstack-dev] [nova] blueprint about multiple workers
> supported   in nova-scheduler
> >>
> >> Hi all,
> >>
> >> I want to make it easy to launch a bunch of scheduler processes on a
> host,
> >> multiple scheduler workers will make use of multiple processors of host
> and
> >> enhance the performance of nova-scheduler.
> >>
> >> I had registered a blueprint and commit a patch to implement it.
> >>
> https://blueprints.launchpad.net/nova/+spec/scheduler-multiple-workers-support
> >>
> >> This patch had applied in our performance environment and pass some test
> >> cases, like: concurrent booting multiple instances, currently we didn't
> find
> >> inconsistent issue.
> >>
> >> IMO, nova-scheduler should been scaled horizontally on easily way, the
> >> multiple workers should been supported as an out of box feature.
> >>
> >> Please feel free to discuss this feature, thanks.
> >>
> >> Best Regards
> >>
> >>
> >>
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