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

Alexei Kornienko alexei.kornienko at gmail.com
Fri Jun 27 14:23:23 UTC 2014


Why should we create queue in advance?

Let's consider following use cases:
* listener starts and creates a queue
* publishers connect to exchange and start publishing

No need to create a queue in advance here since listener does it when it 

* publishers create a queue in advance and start publishing

Creation is not correct since there is no guarantee that someone would 
ever use this queue...

IMHO listener should create a queue and publishers should not care about 
it at all.

What do you think?

On 06/27/2014 05:16 PM, Sandy Walsh wrote:
> Something to consider is the "create the queue in advance" feature is 
> done for notifications, so we don't drop important messages on the 
> floor by having an Exchange with no associated Queue.
> For RPC operations, this may not be required (we assume the service is 
> available). If this check is truly a time-sink we could ignore that 
> check for rpc calls.
> -S
> On 6/10/2014 9:31 AM, Alexei Kornienko wrote:
>> Hi,
>> Please find some answers inline.
>> Regards,
>> Alexei
>> On 06/10/2014 03:06 PM, Flavio Percoco wrote:
>>> On 10/06/14 15:03 +0400, 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.
>>> To some extent, the executors are part of the server class since the
>>> later is the one actually controlling them. If I understood your
>>> proposal, the server class would implement the event loop, which means
>>> we would have an EventletServer / BlockingServer, right?
>>> If what I said is what you meant, then I disagree. Executors keep the
>>> eventloop isolated from other parts of the library and this is really
>>> important for us. One of the reason is to easily support multiple
>>> python versions - by having different event loops.
>>> Is my assumption correct? Could you elaborate more?
>> No It's not how we plan it. Server will do the loop and pass received 
>> message to dispatcher and executor. It means that we would still have 
>> blocking executor and eventlet executor in the same server class. We 
>> would just change the implementation part to make it more consistent 
>> and easier to control.
>>>> 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.
>>> This was done on purpose. The idea was to focus on backwards
>>> compatibility rather than cleaning up/improving the drivers. That
>>> said, sounds like those drivers could user some clean up. However, I
>>> think we should first extend the test suite a bit more before hacking
>>> the existing drivers.
>>>> 3) If we'll separate RPC functionality and messaging functionality 
>>>> it'll make
>>>> code base clean and easily reused.
>>> What do you mean with this?
>> We mean that current drivers are written with RPC code hardcoded 
>> inside (ReplyWaiter, etc.). Thats not how messaging library is 
>> supposed to work. We can move RPC to a separate layer and this would 
>> be beneficial for both rpc (code will become more clean and less 
>> error-prone) and core messaging part (we'll be able to implement 
>> messaging in way that will work much faster).
>>>> 4) Connection pool can be refactored to implement more efficient 
>>>> connection
>>>> reusage.
>>> Please, elaborate. What changes do you envision?
>> Currently there is a class that is called ConnectionContext that is 
>> used to manage pool. Additionaly it can be accessed/configured in 
>> several other places. If we refactor it a little bit it would be much 
>> easier to use connections from the pool.
>>> As Dims suggested, I think filing some specs for this (and keeping the
>>> proposals separate) would help a lot in understanding what the exact
>>> plan is.
>>> Glad to know you're looking forward to help improving oslo.messaging.
>>> Thanks,
>>> Flavio
>>>> 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.
>>>> Thanks!
>>>> [1] https://docs.google.com/document/d/
>>>> 1ARpKiYW2WN94JloG0prNcLjMeom-ySVhe8fvjXG_uRU/edit?usp=sharing
>>>> [2] https://review.openstack.org/#/q/
>>>> status:open+owner:akornienko+project:openstack/oslo.messaging,n,z
>>>> Best regards,
>>>> Dina Belova
>>>> Software Engineer
>>>> Mirantis Inc.
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