I agree with Winson's points. Inline.

On Feb 24, 2014, at 8:31 PM, Renat Akhmerov <[email protected]> wrote:

> 
> On 25 Feb 2014, at 07:12, W Chan <[email protected]> wrote:
> 
>> As I understand, the local engine runs the task immediately whereas the 
>> scalable engine sends it over the message queue to one or more executors.  
> 
> Correct.

Note: that "local" is confusing here, "in process" will reflect what it is 
doing better. 

> 
>> In what circumstances would we see a Mistral user using a local engine 
>> (other than testing) instead of the scalable engine?
> 
> Yes, mostly testing we it could be used for demonstration purposes also or in 
> the environments where installing RabbitMQ is not desirable.
> 
>> If we are keeping the local engine, can we move the abstraction to the 
>> executor instead, having drivers for a local executor and remote executor?  
>> The message flow from the engine to the executor would be consistent, it's 
>> just where the request will be processed.  
> 
> I think I get the idea and it sounds good to me. We could really have 
> executor in both cases but the transport from engine to executor can be 
> different. Is that what you’re suggesting? And what do you call driver here?

+1 to "abstraction to the executor", indeed the local and remote engines today 
differ only by how they invoke executor, e.g. transport / driver.

> 
>> And since we are porting to oslo.messaging, there's already a fake driver 
>> that allows for an in process Queue for local execution.  The local executor 
>> can be a derivative of that fake driver for non-testing purposes.  And if we 
>> don't want to use an in process queue here to avoid the complexity, we can 
>> have the client side module of the executor determine whether to dispatch to 
>> a local executor vs. RPC call to a remote executor.
> 
> Yes, that sounds interesting. Could you please write up some etherpad with 
> details explaining your idea?
> 
> 
> 
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