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)" < > firstname.lastname@example.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 > >> > >> > >> > __________________________________________________________________________ > >> OpenStack Development Mailing List (not for usage questions) > >> Unsubscribe: > openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > > > > __________________________________________________________________________ > > OpenStack Development Mailing List (not for usage questions) > > Unsubscribe: > openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > __________________________________________________________________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev >
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