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From Chamikara Jayalath <chamikar...@gmail.com>
Subject Re: [Sandesha2] Acknowledging policy
Date Tue, 10 Jan 2006 05:24:52 GMT
On 1/9/06, Aleksander Slominski <aslom@cs.indiana.edu> wrote:
>
> Chamikara Jayalath wrote:
>
> > Hi Alec,
> >
> > See my comments below.
> >
> > On 1/9/06, *Aleksander Slominski* < aslom@cs.indiana.edu
> > <mailto: aslom@cs.indiana.edu>> wrote:
> >
> >     hi,
> >
> >     my comments below.
> >
> >     Chamikara Jayalath wrote:
> >
> >>             ----- Original Message -----
> >>             *From:* Chamikara Jayalath <mailto:chamikaramj@gmail.com>
> >>             *To:* sandesha-dev@ws.apache.org
> >>             <mailto: 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.
> >
> >     i am not sure but it looks to me that those are two different
> >     levels of reliability: reliable *message* delivery and reliable
> >     *service invocation*. the former is what i though WS-RM is for and
> >     the latter is not supported in WS-RM unless some special QoS
> >     (Policy?) is used?
> >
> >
> >
> >
> >
> > What  I was  thinking abt was the usability. Most of the time the
> > client may be unaware weather the service has implemented persistent
> > reliability or not. Also at times they may want to make sure that the
> > service actually got invoked before proceeding.Since we are able to
> > provide that, why not add the feature.
>
> AFAICT it will make Sandesha work in different ways from other WS-RM
> implementations as it is an extension.
>
> moreover in-most case this feature ("reliable invocation") is better
> supported (and more interoperable) by having a service sending a
> reliably response message (with "OK" or SOAP:Fault) ...
>
> >
> >     i think that in case of in-memory storage not much can be done for
> >     reliability but ask user to buy UPS :)
> >
> >
> >
> > Ya, that solves the prob. Bit costly though :-)
>
> UPSes are cheap and without them server will not be very reliable anyway
> if it keeps all data in memory - what if it needs to be rebooted ...
>
> >
> >
> >     IMHO the in-memory storage should be not a default in Sandesha2 as
> >     it does not meet requirements of WS-RM instead some persistent
> >     storage should be a default one - maybe just using text files to
> >     store message (as even embedded RDBMS may be overkill for simple
> >     installations)?
> >
> >
> >
> > You have a point. But there may be many users who need an hi
> > performing in-memory case. Those who need persistence (RDBMS or file
> > based) can do it by a single property change..
>
> there is clearly a trade-off between reliability and performance -
> however i am not sure if in-memory storage is good enough to call it
> "reliable"? what should happen when there are many ack-ed but not yet
> processed messages (for example with out-of-order messages) and server
> goes down? those messages will be essentially lost when server (or
> client) that is using in-memory storage crashed and is restarted (for
> perfect reliability TX are needed to be able to rollback in-progress
> unfinished invocations ...)



That is exactly the feature I'm talking abt. With this Sandesha2 will not
ack without invoking the message even in the in-memory case. We can also
make this optional so that users who need acks quickly can get them before
invocation (this will be the default).

Thanx,
Chamikara

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