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From Chamikara Jayalath <chamikar...@gmail.com>
Subject Re: [Sandesha2] Acknowledging policy
Date Sun, 08 Jan 2006 04:56:30 GMT
Hi Jaliya, All,

See my comments below


 ----- Original Message -----
> *From:* Chamikara Jayalath <chamikaramj@gmail.com>
> *To:* sandesha-dev@ws.apache.org
> *Sent:* Friday, January 06, 2006 3:06 AM
> *Subject:* [Sandesha2] Acknowledging policy
>
> Hi All,
>
> It seems like we need to do some adjustments to our acknowledging policy.
>
> Currently acknowledging incoming application messages is done by the
> SandeshaInHandler. So acknowledging happens before the message is actually
> delivered to the service.
>
> >>But the message is received by the RMEndpoint and that means we should
> acknowledge.
>
> But it seems like we can provide a better quality reliability by not
> acknowledging till we actually invoke the service. This way we can guarantee
> the delivering of the message to the service even in the in-memory case. (
> I.e. if the client receive an ack he can be sure that the service got
> actually invoked).
>
> >>Yes, but the problem is once the message is received by the RMEndpoint
> it is RMEndpoints responsibility to invoke the web service. So what we want
> >>is to improve the reliability of the RMEndpoint.
> >>IMHO we should not expect the initial sender to wait till the web
> service gets invoked for an acknowledgment.
> >>Consider a scenario where we have 3 messages and the RMEndpoint manager
> in the destination receive 2 and 3 but not 1. We use INORDER >>invocation.
> Now we will not acknowledge for any of the messages since we did not receive
> message 1. This is not correct, because then the >>RMEndpoint manager in the
> client side will keep on sending all the 3 messages again and again.
>
>

yes, But if the server sends the messages and fail before he actually invoke
the service, the client will proceed believing that the service got actually
invoked. It is not important weather the message got lost in the wire, or it
got lost within the server, the result is the same (the service did not get
invoked). So the result is equal to acknowledging a message the server did
not receive.
But performance wise what you say is very correct. If the server consume a
long time to invoke the service, the client will also have to wait a long
time for an acknowledgement.


Now an interesting problem arises when we consider the implementation of the
> above scenario. Suppose a message arrives to an RM enabled In-Only
> operation. Now SandeshaOutHandler does not get called and we have to send
> the ack within the in-path. How can we do something after invocation within
> the in-path. Here is one way,
>
> Currently we do in-order invocation using the InOrderInvoker thread.
> Within the SandeshaInHandler we pause the messages, and the InOrderInvoker
> resumes them in the correct order. If we make this thread the Invoker for
> all the messages and if we move the ack sending logic into this, we can
> accomplish above (basically we will pause all the incoming messages and we
> will send the ack only after the Invoker thread resumes the message).
>
> But when we consider the current implementation of the pause functionality
> of Axis2 there is again a slight problem. When pause is called the incoming
> thread simply returns. So we have to add the ack before pausing if the
> acksTo endpoint is the anonymous URL.
>
> Considering all of the above points I thought we can go for the policy
> given below.
>
> 1. Sandesa2 will always use the Invoker thread to invoke messages. All
> incoming request messages will be paused in the request path and they will
> be resumed by the Invoker thread.
>
> 2. If the acksTo endpoint is anonymous Sandesha2 will send the
> acknowledgement within the SandeshaInHandler (before actually invoking the
> service.)
>
> 3. If the user has given an actual acksTo endpoint. Sandesha2 will make
> sure that it only acknowledges messages after the invocation.
> >>I think we should have a consistent acknowledgement mechanism in all the
> cases.
>
>
Agree.But I feel it is consistent enough. We can clearly say that the client
can get a better quality reliability (even in the in-memory case) if he
specify a true acksTo endpoint (let's document this well :-) ). I feel it is
better than giving a lower quality in both cases.


Remember that I'm only talking about the in-memory scenarios here. If the
> user go for permanent storage based reliability, invocation of acked
> messages will always be guaranteed (using message re-injection).
>
> >>Let's try to get this working. So we have the maximum reliability :)
>
>
It is already working. But the prob  is code  is  dependent on Hibernate so
I'm not able to commit  the permanent storage pluging. I'll try to create
another plugin using Apache JDO.


Thanx,
Chamikara

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