On Wed, May 24, 2023 at 12:26 AM Felix Huettner via discuss < ovs-discuss@openvswitch.org> wrote: > > Hi Ilya, > > thank you for the detailed reply > > On Tue, May 23, 2023 at 05:25:49PM +0200, Ilya Maximets wrote: > > On 5/23/23 15:59, Felix Hüttner via discuss wrote: > > > Hi everyone, > > > > Hi, Felix. > > > > > > > > we are currently running an OVN Deployment with 450 Nodes. We run a 3 node cluster for the northbound database and a 3 nodes cluster for the southbound database. > > > Between the southbound cluster and the ovn-controllers we have a layer of 24 ovsdb relays. > > > The setup is using TLS for all connections, however the TLS Server is handled by a traefik reverseproxy to offload this from the ovsdb > > > > The very important part of the system description is what versions > > of OVS and OVN are you using in this setup? If it's not latest > > 3.1 and 23.03, then it's hard to talk about what/if performance > > improvements are actually needed. > > > > We are currently running ovs 3.1 and ovn 22.12 (in the process of > upgrading to 23.03). `monitor-all` is currently disabled, but we want to > try that as well. > Hi Felix, did you try upgrading and enabling "monitor-all"? How does it look now?
> > > Northd and Neutron is connecting directly to north- and southbound databases without the relays. > > > > One of the big things that is annoying is that Neutron connects to > > Southbound database at all. There are some reasons to do that, > > but ideally that should be avoided. I know that in the past limiting > > the number of metadata agents was one of the mitigation strategies > > for scaling issues. Also, why can't it connect to relays? There > > shouldn't be too many transactions flowing towards Southbound DB > > from the Neutron. > > > > Thanks for that suggestion, that definately makes sense. > Does this make a big difference? How many Neutron - SB connections are there? What rings a bell is that Neutron is using the python OVSDB library which hasn't implemented the fast-resync feature (if I remember correctly). At the same time, there is the feature leader-transfer-for-snapshot, which automatically transfer leader whenever a snapshot is to be written, which would happen frequently if your environment is very active. When a leader transfer happens, if Neutron set the option "leader-only" (only connects to leader) to SB DB (could someone confirm?), then when the leader transfer happens, all Neutron workers would reconnect to the new leader. With fast-resync, like what's implemented in C IDL and Go, the client that has cached the data would only request the delta when reconnecting. But since the python lib doesn't have this, the Neutron server would re-download full data when reconnecting ... This is a speculation based on the information I have, and the assumptions need to be confirmed. > > > > > > We needed to increase various timeouts on the ovsdb-server and client side to get this to a mostly stable state: > > > * inactivity probes of 60 seconds (for all connections between ovsdb-server, relay and clients) > > > * cluster election time of 50 seconds > > > > > > As long as none of the relays restarts the environment is quite stable. > > > However we see quite regularly the "Unreasonably long xxx ms poll interval" messages ranging from 1000ms up to 40000ms. > > > > With latest versions of OVS/OVN the CPU usage on Southbound DB > > servers without relays in our weekly 500-node ovn-heater runs > > stays below 10% during the test phase. No large poll intervals > > are getting registered. > > > > Do you have more details on under which circumstances these > > large poll intervals occur? > > > > It seems to mostly happen on the initial connection of some client to > the ovsdb. From the few times we ran perf there it looks like the time > is spend in creating a monitor and during that sending out the updates > to the client side. > It is one of the worst case scenario for OVSDB when many clients initialize connections to it at the same time, when the size of data downloaded by each client is big. OVSDB relay, for what I understand, should greatly help on this. You have 24 relay nodes, which are supposed to share the burden. Are the SB DB and the relay instances running with sufficient CPU resources? Is it clear that initial connections from which clients (ovn-controller or Neutron) are causing this? If it is Neutron, the above speculation about the lack of fast-resync from Neutron workers may be worth checking. > If it is of interest i can try and get a perf report once this occurs > again. > > > > > > > If a large amount of relays restart simultaneously they can also bring the ovsdb cluster to fail as the poll interval exceeds the cluster election time. > > > This happens with the relays already syncing the data from all 3 ovsdb servers. > > > > There was a performance issue with upgrades and simultaneous > > reconnections, but it should be mostly fixed on the current master > > branch, i.e. in the upcoming 3.2 release: > > https://patchwork.ozlabs.org/project/openvswitch/list/?series=348259&state=* > > > > That sounds like that might be similar to when our issue occurs. I'll > see if we can try this out. > > > > > > > We would like to improve this significantly to ensure on the one hand that our ovsdb clusters will survive unplanned load without issues and on the other hand to keep the poll intervals short. > > > We would like to ensure a short poll interval to allow us to act on distributed-gateway-ports failovers and failover of virtual port in a timely manner (ideally below 1 second). > > > > These are good goals. But are you sure they are not already > > addressed with the most recent versions of OVS/OVN ? > > > > I was not sure, but all your feedback helped clarifying that. > > > > > > > To do this we found the following solutions that were discussed in the past: > > > 1. Implementing multithreading for ovsdb https://patchwork.ozlabs.org/project/openvswitch/list/?series=&submitter=&state=*&q=multithreading&archive=&delegate= > > > > We moved the compaction process to a separate thread in 3.0. > > This partially addressed the multi-threading topic. General > > handling of client requests/updates in separate threads will > > require significant changes in the internal architecture, AFAICT. > > So, I'd like to avoid doing that unless necessary. So far we > > were able to overcome almost all the performance challenges > > with simple algorithmic changes instead. > > > > I definately get that since that would be quite a complex change to do. > The only benefit i would see in having clients in separate threads is > that it reduces the impact of performance challenges. > E.g. it would still allow the cluster to healthly work together and make > progress, but individual reconnects would be slow. > > That benefit would be quite significant from my perspective as it makes > the solution more resillient. But i'm not sure if its worth the > additional complexity. > Multithreading for general OVSDB tasks (transactions, monitoring) seems more complex to implement, and the outcome should be very similar to OVSDB relay (which is multi-process instead of multi-threading), except that multi-threading may have a smaller memory footprint. Multithreading for RAFT cluster RPC may help keeping the cluster healthy when server load is high, but the same can be achieved by setting a longer election timer. I agree there is a subtle difference when you want fast failure detection for things like node crash but can tolerate overloaded servers that can barely respond to clients. Looking forward to hearing back from you regarding the situation. Thanks, Han > > > 2. Changing the storage backend of OVN to an alternative (e.g. etcd) https://mail.openvswitch.org/pipermail/ovs-discuss/2016-July/041733.html > > > > There was an ovsdb-etcd project, but it didn't manage to provide > > better performance in comparison with ovsdb-server. So it was > > ultimately abandoned: https://github.com/IBM/ovsdb-etcd > > > > > > > > Both of these discussion are from 2016, not sure if more up-to-date ones exist. > > > > > > I would like to ask if there are already existing discussions on scaling ovsdb further/faster? > > > > This again comes to a question what versions you're using. I'm > > currently not aware of any major performance issues for ovsdb-server > > on the most recent code, besides the conditional monitoring, which is > > not entirely OVSDB server's issue. And it is also likely to become > > a bit better in 3.2: > > https://patchwork.ozlabs.org/project/openvswitch/patch/20230518121425.550048-1-i.maxim...@ovn.org/ > > > > That also sounds like a quite interesting change that might help us > here. > > > > > > > From my perspective whatever such a solution might be, would no longer require relays and allow the ovsdb servers to handle load gracefully. > > > I personally see that multithreading for ovsdb sounds quite promising, as that would allow us to separate the raft/cluster communication from the client connections. > > > This should allow us to keep the cluster healthly even under significant pressure of clients. > > > > Again, good goals. I'm just not sure if we actually need to do > > something or if they are already achievable with the most recent code. > > > > I understand that testing on prod is not an option, so it's unlikely > > we'll have an accurate test. But maybe you can participate in the > > initiative [1] for creation of ovn-heater OpenStack scenarios that > > might be close to workloads you have? This way upstream will be able > > to test your use-cases or at least something similar. > > > > Most of our current efforts are focused on ovn-kubernetes use-case, > > because we don't have much details on how high-scale OpenStack deployments > > look like. > > > > [1] https://mail.openvswitch.org/pipermail/ovs-dev/2023-May/404488.html > > > > That looks very interesting and would also help us running scale tests. > I'll get in contact with whoever is working on that to help out as well. > > > Best regards, Ilya Maximets. > > > > > > > > Thank you > > > > > > -- > > > Felix Huettner > > > > Thanks for all of the detailed insights. > Felix > Diese E Mail enthält möglicherweise vertrauliche Inhalte und ist nur für die Verwertung durch den vorgesehenen Empfänger bestimmt. > Sollten Sie nicht der vorgesehene Empfänger sein, setzen Sie den Absender bitte unverzüglich in Kenntnis und löschen diese E Mail. > > Hinweise zum Datenschutz finden Sie hier<https://www.datenschutz.schwarz>. > > > This e-mail may contain confidential content and is intended only for the specified recipient/s. > If you are not the intended recipient, please inform the sender immediately and delete this e-mail. > > Information on data protection can be found here< https://www.datenschutz.schwarz>. > _______________________________________________ > discuss mailing list > disc...@openvswitch.org > https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
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