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Subject: Re: [ws-rx] NEW ISSUE: Remove LastMessage
I agree. I don't quite grok what is meant by 'filling gaps before the Sequence is terminated' and how LM helps in this regard. Filling gaps is part of the protocol and if there are gaps the RMS won't terminate the sequence (since all the acks won't be received) -- baring non-normal termination. -Anish -- Christopher B Ferris wrote: > > What do you mean "fill gaps"? An RMD "fills gaps" by sending SeqAcks with > gaps that the RMS subsequently retransmits. LM is not relevant to this > aspect > of the protocol. > > 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 > > "Yalcinalp, Umit" <umit.yalcinalp@sap.com> wrote on 11/30/2005 06:34:18 PM: > > > 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 > willremember > > > > > 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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