[openstack-dev] [oslo][messaging] Further improvements and refactoring

Alexei Kornienko alexei.kornienko at gmail.com
Tue Jun 10 13:40:00 UTC 2014

On 06/10/2014 03:59 PM, Gordon Sim wrote:
> On 06/10/2014 12:03 PM, Dina Belova wrote:
>> Hello, stackers!
>> Oslo.messaging is future of how different OpenStack components
>> communicate with each other, and really I’d love to start discussion
>> about how we can make this library even better then it’s now and how can
>> we refactor it make more production-ready.
>> As we all remember, oslo.messaging was initially inspired to be created
>> as a logical continuation of nova.rpc - as a separated library, with
>> lots of transports supported, etc. That’s why oslo.messaging inherited
>> not only advantages of now did the nova.rpc work (and it were lots of
>> them), but also some architectural decisions that currently sometimes
>> lead to the performance issues (we met some of them while Ceilometer
>> performance testing [1] during the Icehouse).
>> For instance, simple testing messaging server (with connection pool and
>> eventlet) can process 700 messages per second. The same functionality
>> implemented using plain kombu (without connection pool and eventlet)
>> driver is processing ten times more - 7000-8000 messages per second.
>> So we have the following suggestions about how we may make this process
>> better and quicker (and really I’d love to collect your feedback, 
>> folks):
>> 1) Currently we have main loop running in the Executor class, and I
>> guess it’ll be much better to move it to the Server class, as it’ll make
>> relationship between the classes easier and will leave Executor only one
>> task - process the message and that’s it (in blocking or eventlet mode).
>> Moreover, this will make further refactoring much easier.
>> 2) Some of the drivers implementations (such as impl_rabbit and
>> impl_qpid, for instance) are full of useless separated classes that in
>> reality might be included to other ones. There are already some changes
>> making the whole structure easier [2], and after the 1st issue will be
>> solved Dispatcher and Listener also will be able to be refactored.
>> 3) If we’ll separate RPC functionality and messaging functionality it’ll
>> make code base clean and easily reused.
>> 4) Connection pool can be refactored to implement more efficient
>> connection reusage.
>> Folks, are you ok with such a plan? Alexey Kornienko already started
>> some of this work [2], but really we want to be sure that we chose the
>> correct vector of development here.
> For the impl_qpid driver, I think there would need to be quite 
> significant changes to make it efficient. At present there are several 
> synchronous roundtrips for every RPC call made[1]. Notifications are 
> not treated any differently than RPCs (and sending a call is no 
> different to sending a cast).
> I agree the connection pooling is not efficient. For qpid at least it 
> creates too many connections for no real benefit[2].
> I think this may be a result of trying to fit the same high-level 
> design to two entirely different underlying APIs.
> For me at least, this also makes it hard to spot issues by reading the 
> code. The qpid specific 'unit' tests for oslo.messaging also fail for 
> me everytime when an actual qpidd broker is running (I haven't yet got 
> to the bottom of that).
> I'm personally not sure that the changes to impl_qpid you linked to 
> have much impact on either efficiency or readability, safety of the code. 
Indeed it was only to remove some of the unnecessary complexity of the 
code. We'll see more improvement after we'll implement points 1,2 from 
the original email (cause the will allow us to proceed to further 

> I think there could be a lot of work required to significantly improve 
> that driver, and I wonder if that would be better spent on e.g. the 
> AMQP 1.0 driver which I believe will perform much better and will 
> offer more choice in deployment.
I agree with you on this. However I'm not sure that we can do such a 
decision. If we focus on amqp driver only we should mention it 
explicitly and deprecate qpid driver completely. There is no point in 
keeping driver that is not really functional.
> --Gordon
> [1] For both the request and the response, the sender is created every 
> time, which results in at least one roundtrip to the broker. Again, 
> for both the request and the response, the message is then sent with a 
> blocking send, meaning a further synchronous round trip for each. So 
> for an RPC call, instead of just one roundtrip, there are at least four.
> [2] In my view, what matters more than per-connection throughput for 
> olso.messaging, is the scalability of the system as you add many RPC 
> clients and servers. Excessive creation of connections by each process 
> will have a negative impact on this. I don't believe the current code 
> gets anywhere close to the limits of the underlying connection and 
> suspect it would be more efficient and faster to multiplex different 
> streams down the same connection. This would be especially true where 
> using eventlet I suspect.
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