Re: [ws-rx] NEW ISSUE: Remove LastMessage

[Doug Davis <dug@us.ibm.com>]

Anish,
  I think your argument actually
adds to the reasons why it should be removed  :-)
You're placing some additional semantics
on the LastMessage marker that are not in the
spec and removing this marker would
remove the possibility of others reading too much 
into it too.

  The LastMessage marker has no
impact on the termination of the sequence.  Even
if the RMD gets a LastMessage marker
but not a Terminate, and it chooses to timeout
the sequence, its still an abnormal
termination.  The only non-abnormal termination
is when the RMD receives a Terminate
from the RMS.  And,either way, the RMD needs
to keep the sequence state around until
it gets a Terminate or it decides to terminate it 
on its own.  Receipt of a LastMessage
does not change this.  Ultimately, its up to the
RMS to decide whether or not a sequence
needs to have some kind of error recovery
done, not the RMD, and this would be
based on the Acks it receives and not the delivery 
of a Terminate (or LastMessage marker)
 to the RMD.

  As to freeing up some resources,
the LastMessage doesn't change this either. The data
an RMD retains isn't dependent on the
LastMessage.  You seem to indicate that the RMD
can free up some stuff base on this
marker - this isn't true.  There are no new resources that
it can drop based on it.  It must
still maintain the ack state in case an AckReq comes in.
If there are some other bits of data
that it can now forget about I would claim that it could have
forgotten about them even w/o the LastMessage
marker.

thanks
-Doug

Anish Karmarkar <Anish.Karmarkar@oracle.com>

11/02/2005 09:54 PM

To	Marc Goodner <mgoodner@microsoft.com>
cc	Jacques Durand <JDurand@us.fujitsu.com>, Doug Davis/Raleigh/IBM@IBMUS, ws-rx@lists.oasis-open.org
Subject	Re: [ws-rx] NEW ISSUE: Remove LastMessage

Our (Oracle) email server is having some problems
(delays) with 
delivering external emails intermittently since yesterday. I'm therefore
relying on the OASIS email archive [1], which is not very reliable 
(based on the complaints that I have seen on this list -- ironic given
the work that this TC is doing ;-) ). Apologies if I missed emails in 
this thread that already repeat/refute the argument below.

I don't think we should remove the LastMessage marker, but not for the
reasons that Marc is stating (security/consistency). I quite agree with
Doug on the security/consistency part. The LastMessage marker serves a
very important purpose:

Under non-failure/normal operating conditions, there would not be a 
CloseSequence message sent. The Sequence would start with CS/CSR 
messages followed by Seq/SeqAck/SeqNack/ReqForAck messages and end with
TerminateSequence message. The TerminateSequence message does not 
contain the last sequence number and is a message that can get lost (is
not reliable).

If the TerminateSequence message is not received by the RMD and the 
LastMessage marker is *not* present in the last message of the sequence,
the RMD has to hang around and keep its resources around until it times
out. Once it times out it is going to assume (incorrectly) an abnormal
termination of the sequence (and perhaps take corrective action).

If the TerminateSequence message is not received by the RMD and the 
LastMessage marker *is* present in the last message of the sequence, the
RMD knows that it is done with the sequence and has to only be around to
receive the final terminate message (or request for acks/re-ack, if any
ack was lost) and may free up some of its resources. In this case, the
loss of the TerminateSequence message does not result in an abnormal 
termination of the sequence on the RMD side on time out and no 
corrective action is necessary on the RMD side.

If the LastMessage marker is removed, there is a possibility (when the
TerminateSequence message is lost) that the RMD may abnormally terminate
the sequence when in fact it is not necessary to do so.

Hope that makes sense.

Thx.

-Anish
--

[1] http://www.oasis-open.org/apps/org/workgroup/ws-rx/messages.php


Marc Goodner wrote:
> I’m not so sure. I need to think about this some more.
> 
>  
> 
> A couple of observations though. First removing this breaks at least
one 
> point of consistency with the contributed spec. I suggest we think
> carefully before doing that. Second I don’t see this as a “protocol
> complexity” issue. While the Close operation could completely subsume
> the LastMessage marker you can still use this marker today without
using 
> Close at all. That seems valuable to retain as it provides a simpler
> protocol interaction capability in normal circmstances.
> 
>  
> 
> I disagree that this should be removed because a security mechanism
can 
> address part of the functionality. I might agree is the composition
with 
> that security mechanism was actually defined. If that is part of the
> rationale for this I suggest not doing this until we have that security
> composition defined.
> 
>  
> 
> ------------------------------------------------------------------------
> 
> *From:* Jacques Durand [mailto:JDurand@us.fujitsu.com]
> *Sent:* Wednesday, November 02, 2005 10:47 AM
> *To:* 'Doug Davis'; ws-rx@lists.oasis-open.org
> *Subject:* RE: [ws-rx] NEW ISSUE: Remove LastMessage
> 
>  
> 
> +1
> 
> I thought about proposing this too. The new Close operation subsumes
> almost completely the LastMessage marker  - the
> 
> added value is not worth the added protocol complexity.
> 
> -Jacques
> 
>  
> 
> ------------------------------------------------------------------------
> 
> *From:* Doug Davis [mailto:dug@us.ibm.com]
> *Sent:* Wednesday, November 02, 2005 7:30 AM
> *To:* ws-rx@lists.oasis-open.org
> *Subject:* [ws-rx] NEW ISSUE: Remove LastMessage
> 
>  
> 
> 
> Title:Remove LastMessage
> 
> Description:
> The LastMessage element, as part of a Sequence header element, appears
> superfluous. It seems to serve 2 purposes:
> 1 - force a SeqAck to be sent back from the RMD
> 2 - force the RMD to reject any messages with a higher message #
> 
> #1 can be done with an AckReq header.  We should avoid having
multiple 
> ways to do the same thing.
> #2 is really only an issue if someone tries to hijack the sequence
- and 
> to protect against that we should be using a real security mechanism
> like WS-SC/Trust, not the LastMessage element.
> 
> When an RMS is done with a sequence it is free to simply Close or
> Terminate it (whether or not it has all of the Acks it wants - but
> normally it will wait) - having an additional message exchange to
send a 
> LastMessage is unnecessary.
> 
> Justification: See above.
> 
> Target: core
> 
> Proposal:  Remove all references to LastMessage (and related
Fault) 
>  from the spec [1].  See attached diff/pdf file for the
specific changes.
> 
> [1] 
> http://www.oasis-open.org/apps/org/workgroup/ws-rx/download.php/15001/wsrm-1.1-spec-wd-05.pdf
> 
> 
> 
> Note the protocol flow/example picture was updated too.
>