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On Fri, May 08, 2015 at 09:13:59AM -0400, Doug Hellmann wrote:
> Excerpts from Joe Gordon's message of 2015-05-07 17:43:06 -0700:
> > On May 7, 2015 2:37 AM, "Sahid Orentino Ferdjaoui" <
> > sahid.ferdjaoui at redhat.com> wrote:
> > >
> > > Hi,
> > >
> > > The primary point of this expected discussion around asynchronous
> > > communication is to optimize performance by reducing latency.
> > >
> > > For instance the design used in Nova and probably other projects let
> > > able to operate ascynchronous operations from two way.
> > >
> > > 1. When communicate between inter-services
> > > 2. When communicate to the database
> > >
> > > 1 and 2 are close since they use the same API but I prefer to keep a
> > > difference here since the high level layer is not the same.
> > >
> > > From Oslo Messaging point of view we currently have two methods to
> > > invoke an RPC:
> > >
> > >   Cast and Call: The first one is not bloking and will invoke a RPC
> > >     without to wait any response while the second will block the
> > >     process and wait for the response.
> > >
> > > The aim is to add new method which will return without to block the
> > > process an object let's call it "Future" which will provide some basic
> > > methods to wait and get a response at any time.
> > >
> > > The benefice from Nova will comes on a higher level:
> > >
> > > 1. When communicate between services it will be not necessary to block
> > >    the process and use this free time to execute some other
> > >    computations.
> > 
> > Isn't this what the use of green threads (and eventlet) is supposed to
> > solve. Assuming my understanding is correct, and we can fix any issues
> > without adding async oslo.messaging, then adding yet another async pattern
> > seems like a bad thing.

The aim is to be not library specific and avoid to add different and
custom patterns on the base code each time we want something not
blocking.
We can let the well experimented community working in olso messaging
to maintain that part and as Doug said oslo can use different
"executors" so we can avoid the requirement of a specific library.

> Yes, this is what the various executors in the messaging library do,
> including the eventlet-based executor we use by default.
> 
> Where are you seeing nova block on RPC calls?

In Nova we use the indirection api to make call to the database by the
conductor through RPCs.
By the solution	presented we can create async operations to read and
write from the database.

Olekssi asks me to give an example I will reply to him.

s.
> Doug
> 
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