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Subject: RE: [ws-rx] NEW ISSUE: Remove LastMessage
- From: Doug Davis <dug@us.ibm.com>
- To: ws-rx@lists.oasis-open.org
- Date: Wed, 30 Nov 2005 18:59:33 -0500
Ah - I think I understand what you mean
- ignore my previous note.
If we wanted to explore a "gap-filling"
feature wouldn't that need to be initiated by the RMS and wouldn't that
probably be based on the Acks the RMS had received? So, since the
lastMessage marker wouldn't change the Acks the RMD sends back would it
have any impact on a "gap-filling" solution?
thanks
-Doug
"Yalcinalp, Umit"
<umit.yalcinalp@sap.com>
11/30/2005 06:34 PM
|
To
| Christopher B Ferris/Waltham/IBM@IBMUS,
<ws-rx@lists.oasis-open.org>
|
cc
|
|
Subject
| RE: [ws-rx] NEW ISSUE: Remove
LastMessage |
|
I agree with you that LastMessage
does not change the responsibilities of the RMD. I was more interested
in exploring the utility of using LastMessage from a different angle, as
a clear demarcation point for RMD to allow start filling the gaps in a
sequence before a sequence is terminated. Of course, this hook will only
be useful if there were an architected way for filling the gaps and whether
we want to go there or not...
--umit
From: Christopher B Ferris [mailto:chrisfer@us.ibm.com]
Sent: Wednesday, Nov 30, 2005 5:00 AM
To: ws-rx@lists.oasis-open.org
Subject: Re: [ws-rx] NEW ISSUE: Remove LastMessage
+1
The LastMessage does not change the responsibilities of the RMD. It cannot
free up resources
until it receives either the TerminateSequence or the sequence expires.
Whether or not the
LastMessage is ever received by the RMD, it must still wait for one of
those events before
reclaiming resources.
Cheers,
Christopher Ferris
STSM, Emerging e-business Industry Architecture
email: chrisfer@us.ibm.com
blog: http://webpages.charter.net/chrisfer/blog.html
phone: +1 508 377 9295
Doug Davis/Raleigh/IBM@IBMUS wrote on 11/30/2005 04:38:23 AM:
>
> Anish,
> more inline - I think we're getting closer :-)
> -Doug
>
>
> Anish Karmarkar <Anish.Karmarkar@oracle.com> wrote on 11/29/2005
10:43:05 PM:
>
> > Hey Doug,
> >
> > More comments inlined below.
> >
> > I realize that I'm picking on an optimization feature which is
> > applicable only a certain scenario. But I want to explore this
to ensure
> > that we are indeed doing the right thing. One of the reasons
I'm
> > concerned about this optimization feature is because a Sequence
may not
> > have an expiration time (PTOS), in which case the loss of the
unreliable
> > SequenceTermination message may result in the RMD holding on
to the
> > message queue much longer than needed. More below.
> > Thx!
> >
> > -Anish
> > --
> >
> > Doug Davis wrote:
> > >
> > > Anish,
> > > comment inline.
> > > thanks
> > > -Doug
> > >
> > > Anish Karmarkar <Anish.Karmarkar@oracle.com> wrote
on 11/28/2005
> > > 09:48:10 PM:
> > >
> > > > I thought this issue arose because of the addition
of the Close message
> > > > and I'm not sure why the Close message changes
anything wrt LastMessage
> > > > marker.
> > >
> > > I actually agree. I don't think Close changes the
need for (or lack of
> > > a need
> > > for) LastMessage but if it help convince others then ok
;-)
> > >
> > > > > I think your argument actually adds
to the reasons why itshould 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.
> > > > You are right that the spec does not explicitly
say that but it seems
> > > > like a corollary to what the spec says.
> > >
> > > Not to me - and this ambiguity is part of the reason to
remove it.
> > >
> >
> > Not sure what additional semantics I'm placing on LastMessage
marker.
> > If I get a message with LastMessage marker, I know that this
is the last
> > message in the sequence => RMD cannot get a message with SeqNo
larger
> > than the SeqNo of the message containing LastMessage marker.
>
> Yes - as I noted in the original issue text this would just prevent
the
> RMD from receiving message with a higher #, but that's about it. So,
> if security is the reason for this feature, then its a poor way of
adding
> security and the other means (SC/Trust) are far more appropriate.
>
> > This allows
> > the RMD to shed some resources, if (and only if) it has received
all the
> > messages between SeqNo 1 and the SeqNo of the LastMessage.
> >
> > Perhaps you are referring to my email where I say:
> > "... 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."
> >
> > You are right, that this is an incorrect conclusion to draw.
This would
> > still be an abnormal termination. But that doesn't necessarily
take away
> > the optimization potential at the RMD (assuming all the messages
upto
> > the LastMessage are received).
>
> I'm still not following you. What resources do you think the
RMD can
> shed based on LastMessage? I think the situation you're focusing
on is
> one where all messages have been received by the RMD. So, in
that case
> all you need to keep track of is the highest message number received,
and
> note that you don't really need to keep around anything else - just
the
> number itself. Whether or not this one is tagged as the last
message
> doesn't change that nor can the RMD do anything with that information
> aside from not allow any message with a higher # (as mentioned above).
> But in terms of freeing resources whether or not the RMD can free
any
> resources is not influenced by this additional flag.
>
> > > > > 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.
> > > >
> > > > Quite true, because the RMS may not have received
all the Acks. But the
> > > > RMD may not bother to do anything about it and
leave it to the RMS to
> > > > take correctly action, if necessary. Why is it
that only the RMS can
> > > > initiate corrective action (as you state below)?
Wouldn't
> that depend on
> > > > the application/context.
> > >
> > > Any corrective action an RMD can take (which I think is
limited to
> > > closing or terminating a sequence) is not based on the LastMessage
> > > tag/marker.
> > >
> >
> > Why is that?
> > If the RMD receives all the messages in a Sequence (and it knows
that
> > from the LM marker), and there is a abnormal termination (cause
the RMD
> > did not receive the TerminateSequence message), RMD may decide
not to
> > worry about any corrective action. OTOH, the RMD may decide to
take a
> > corrective action if it knows that it hasn't received all the
messages
> > in the Sequence (and LM is the key in figuring that out).
>
> Ok, so if a sequence has 3 messages there are two situations, one
where
> the LM was sent and one where it was not. And then, in both
cases, there
> is an abnormal termination. I claim that the behavior of the RMS and
RMD
> in both cases would be the same. The RMS, whether or not the
LM was used,
> with either be ok with the ACKs it had received or not. On the
RMD side
> I think you're trying to say that the RMD can think of it as being
"less
> serious" if the highest message was tagged with the LM marker
and therefore
> could just drop the sequence, right?
> I don't think you can make this assumption though. Since the
RMD has not
> received a terminate the only safe thing it can assume is that the
RMS
> has not received all of the ACKs - so while I think what you're saying
is
> that the RMD can drop the seq since it got the LM marker, it can't
since
> it can't make any assuption about what the RMS knows. And, therefore
would
> not be able to drop any more knowledge of the sequence since it must
still
> respond to Close/Terminate messages.
>
> > > > > 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.
> > > >
> > > > But the RMD can relinquish the message store/queue
at this
> point. All it
> > > > has to remember is the Seq Number for the LastMessage.
> > >
> > > What the RMD needs to remember isn't dependent on LastMessage.
Let's say
> > > the RMS sends messages 1, 2 and 3 but 3 is lost. The
RMD will remember
> > > that
> > > 1 and 2 arrived. Upon receipt of an AckReq (w/LastMessage=3)
what will
> > > it do
> > > with this knowledge? Nothing. It will still send back
an Ack with message
> > > numbers 1 and 2. Knowing that the RMS sent any message
# higher than 2
> > > doesn't
> > > change the state information of what the RMD needs to keep
around. How
> > > much
> > > of each message the RMD needs to remember (just state vs
entire message
> > > content)
> > > is more tied to the InOrder flag - so it needs to remember
the entire
> > > message
> > > until the time it can actually deliver the message to the
RMD's app.
> > > Again,
> > > LastMessage has no impact on this.
> > >
> >
> > I didn't quite state the situation correctly:
> > The RMD can relinquish the message store/queue only when it knows
it has
> > received all the messages. This requires that there are no 'holes'
*and*
> > the knowledge of the seqno of the last message.
> > I.e., if a message within the sequence was not received (received
> > messages: 1, 2, 3, 5, 6) then knowing that 6 was the last message
does
> > not provide any ability for the RMD to optimize.
>
> See above - previous comment.
>
> > > > > 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.
> > > >
> > > > Any reason not to relinquish the message store,
close
> > > > connections/sessions, commit transactions etc?
> > >
> > > Perhaps but its not based on LastMessage but rather other
information,
> > > like which messages have arrived and been delivered (as
mentioned above).
> > >
> >
> > So if the RMD has received all the messages (including the last
message
> > in the Sequence) and if the LM marker is not present the RMD
cannot
> > relinquish the message store/connection/session etc unless either
it
> > timesout or expires (and not all Sequences have expiration time)
or the
> > TerminateSequence message (which is unreliable) is received.
>
> See above.
>
> > > > I'm assuming that the motivation for getting
rid of LastMessage marker
> > > > is so that the RMS is not forced to send an additional
empty message
> > > > when it is done. For some applications, it is
not clear which the last
> > > > message with payload is, until it has finished
sending that message.
> > >
> > > I don't think it matters. If after message #3 is sent,
the RMS decides
> > > that that really was the last message then it can send a
Terminate once it
> > > receives the Ack for all messages (1-3). Having to
send an additional
> > > message
> > > to say 'tag message 3 as the last one' doesn't change any
message
> > > processing
> > > logic on either side. In either case the RMD will
still need to
> > > maintain the
> > > exact same state information. I'm claiming that any
information that you
> > > think the RMD can relinquish upon receipt of the LastMessage
could have
> > > been dropped before the receipt of the LastMessage marker.
> > >
> >
> > The RMD cannot drop the message store without the LM marker (assuming
> > that there are no 'holes') unless it receives a TerminateSequence
> > message or timesout/expires.
>
> See above - LM marker doesn't change anything.
>
> > > > What if we were to make the LastMessage marker
optional? Allow RMS to
> > > > include it and the RMD can optimize things based
on the marker if it
> > > > wishes to do so, but not require the RMS to always
send it.
> > >
> > > I still don't see what optimizations you think the RMD can
do with it?
> > > I don't think there are any - which is why I think its a
useless feature.
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