On Fri, 2014-03-21 at 00:32 +0200, Alexei Kornienko wrote: > On 03/21/2014 12:15 AM, Jay Pipes wrote: > > On Fri, 2014-03-21 at 00:03 +0200, Alexei Kornienko wrote: > >> Hello, > >> > >> We've done some profiling and results are quite interesting: > >> during 1,5 hour ceilometer inserted 59755 events (59755 calls to > >> record_metering_data) > >> this calls resulted in total 2591573 SQL queries. > > Yes, this matches my own experience with Ceilo+MySQL. But do not assume > > that there are 2591573/59755 or around 43 queries per record meter > > event. That is misleading. In fact, the number of queries per record > > meter event increases over time, as the number of retries climbs due to > > contention between readers and writers. > > > >> And the most interesting part is that 291569 queries were ROLLBACK > >> queries. > > Yep, I noted that as well. But, this is not unique to Ceilometer by any > > means. Just take a look at any database serving Nova, Cinder, Glance, or > > anything that uses the common SQLAlchemy code. You will see a huge > > percentage of entire number of queries taken up by ROLLBACK statements. > > The problem in Ceilometer is just that the write:read ratio is much > > higher than any of the other projects. > > > > I had a suspicion that the rollbacks have to do with the way that the > > oslo.db retry logic works, but I never had a chance to investigate it > > further. Would be really interested to see similar stats against > > PostgreSQL and see if the rollback issue is isolated to MySQL (I suspect > > it is). > Rollbacks are caused not by retry logic but by create_or_update logic: > We first try to do INSERT in sub-transaction when it fails we rollback > this transaction and do update instead.
No, that isn't correct, AFAIK. We first do a SELECT into the table and then if no result, try an insert: https://github.com/openstack/ceilometer/blob/master/ceilometer/storage/impl_sqlalchemy.py#L286-L292 The problem, IMO, is twofold. There does not need to be nested transactional containers around these create_or_update lookups -- i.e. the lookups can be done outside of the main transaction begin here: https://github.com/openstack/ceilometer/blob/master/ceilometer/storage/impl_sqlalchemy.py#L335 Secondly, given the volume of inserts (that also generate selects), a simple memcache lookup cache would be highly beneficial in cutting down on writer/reader contention in MySQL. These are things that can be done without changing the schema (which has other issues that can be looked at of course). Best, -jay > This is caused by poorly designed schema that requires such hacks. > Cause of this I suspect that we'll have similar results for PostgreSQL. > > Tomorrow we'll do the same tests with PostgreSQL and MongoDB to see if > there is any difference. > > > > > Best, > > -jay > > > >> We do around 5 rollbacks to record a single event! > >> > >> I guess it means that MySQL backend is currently totally unusable in > >> production environment. > >> > >> Please find a full profiling graph attached. > >> > >> Regards, > >> > >> On 03/20/2014 10:31 PM, Sean Dague wrote: > >> > >>> On 03/20/2014 01:01 PM, David Kranz wrote: > >>>> On 03/20/2014 12:31 PM, Sean Dague wrote: > >>>>> On 03/20/2014 11:35 AM, David Kranz wrote: > >>>>>> On 03/20/2014 06:15 AM, Sean Dague wrote: > >>>>>>> On 03/20/2014 05:49 AM, Nadya Privalova wrote: > >>>>>>>> Hi all, > >>>>>>>> First of all, thanks for your suggestions! > >>>>>>>> > >>>>>>>> To summarize the discussions here: > >>>>>>>> 1. We are not going to install Mongo (because "is's wrong" ?) > >>>>>>> We are not going to install Mongo "not from base distribution", > >>>>>>> because > >>>>>>> we don't do that for things that aren't python. Our assumption is > >>>>>>> dependent services come from the base OS. > >>>>>>> > >>>>>>> That being said, being an integrated project means you have to be able > >>>>>>> to function, sanely, on an sqla backend, as that will always be part > >>>>>>> of > >>>>>>> your gate. > >>>>>> This is a claim I think needs a bit more scrutiny if by "sanely" you > >>>>>> mean "performant". It seems we have an integrated project that no one > >>>>>> would deploy using the sql db driver we have in the gate. Is any one > >>>>>> doing that? Is having a scalable sql back end a goal of ceilometer? > >>>>>> > >>>>>> More generally, if there is functionality that is of great importance > >>>>>> to > >>>>>> any cloud deployment (and we would not integrate it if we didn't think > >>>>>> it was) that cannot be deployed at scale using sqla, are we really > >>>>>> going > >>>>>> to say it should not be a part of OpenStack because we refuse, for > >>>>>> whatever reason, to run it in our gate using a driver that would > >>>>>> actually be used? And if we do demand an sqla backend, how much time > >>>>>> should we spend trying to optimize it if no one will really use it? > >>>>>> Though the slow heat job is a little different because the slowness > >>>>>> comes directly from running real use cases, perhaps we should just set > >>>>>> up a "slow ceilometer" job if the sql version is too slow for its > >>>>>> budget > >>>>>> in the main job. > >>>>>> > >>>>>> It seems like there is a similar thread, at least in part, about this > >>>>>> around marconi. > >>>>> We required a non mongo backend to graduate ceilometer. So I don't think > >>>>> it's too much to ask that it actually works. > >>>>> > >>>>> If the answer is that it will never work and it was a checkbox with no > >>>>> intent to make it work, then it should be deprecated and removed from > >>>>> the tree in Juno, with a big WARNING that you shouldn't ever use that > >>>>> backend. Like Nova now does with all the virt drivers that aren't tested > >>>>> upstream. > >>>>> > >>>>> Shipping in tree code that you don't want people to use is bad for > >>>>> users. Either commit to making it work, or deprecate it and remove it. > >>>>> > >>>>> I don't see this as the same issue as the slow heat job. Heat, > >>>>> architecturally, is going to be slow. It spins up real OSes and does > >>>>> real thinks to them. There is no way that's ever going to be fast, and > >>>>> the dedicated job was a recognition that to support this level of > >>>>> services in OpenStack we need to give them more breathing room. > >>>> Peace. I specifically noted that difference in my original comment. And > >>>> for that reason the heat slow job may not be temporary. > >>>>> Architecturally Ceilometer should not be this expensive. We've got some > >>>>> data showing it to be aberrant from where we believe it should be. We > >>>>> should fix that. > >>>> There are plenty of cases where we have had code that passes gate tests > >>>> with acceptable performance but falls over in real deployment. I'm just > >>>> saying that having a driver that works ok in the gate but does not work > >>>> for real deployments is of no more value that not having it at all. > >>>> Maybe less value. > >>>> How do you propose to solve the problem of getting more ceilometer tests > >>>> into the gate in the short-run? As a practical measure l don't see why > >>>> it is so bad to have a separate job until the complex issue of whether > >>>> it is possible to have a real-world performant sqla backend is resolved. > >>>> Or did I miss something and it has already been determined that sqla > >>>> could be used for large-scale deployments if we just fixed our code? > >>> I think right now the ball is back in the ceilometer court to do some > >>> performance profiling, and lets see what comes of that. I don't think > >>> we're getting more test before the release in any real way. > >>> > >>>>> Once we get a base OS in the gate that lets us direct install mongo from > >>>>> base packages, we can also do that. Or someone can 3rd party it today. > >>>>> Then we'll even have comparative results to understand the differences. > >>>> Yes. Do you know which base OS's are candidates for that? > >>> Ubuntu 14.04 will have a sufficient level of Mongo, so some time in the > >>> Juno cycle we should have it in the gate. > >>> > >>> -Sean > >>> > >>> > >>> > >>> _______________________________________________ > >>> OpenStack-dev mailing list > >>> OpenStack-dev@lists.openstack.org > >>> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > >> _______________________________________________ > >> OpenStack-dev mailing list > >> OpenStack-dev@lists.openstack.org > >> http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > > > > > _______________________________________________ > > OpenStack-dev mailing list > > OpenStack-dev@lists.openstack.org > > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev > > > _______________________________________________ > OpenStack-dev mailing list > OpenStack-dev@lists.openstack.org > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev