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Subject: Re: [wsrm] about ordering
Jacques, The rest of this thread seems to be extending the options rather than addressing the questions you raise so I will start back here. I do not believe this proposal aligns with the decisions this group has already made on REL-16 and adds requirements not presently in our Requirements document. In a number of previous discussions, we chose *not* to cover the monitoring (ordered but not guaranteed delivery) use case. This proposal appears to head toward reopening those earlier decisions. thanx, doug On 08-Sep-03 21:15, Jacques Durand wrote: > I propose the following (partial) answer for Rel 57, see below, > and also after this, see my concern on the way we seem to tie the > "ordering" vs "no ordering" decision > to the seq number value (section 9.5 in the meeting minutes) > > Regards, > > jacques > > *Rel 57:* > > *Proposal*: Message ordering has actually two variants (o1) and (o2) > that address different ordering requirts. Roughly: > > - "message ordering" (o1): loosing some messages will not > "break" a sequence, provided that what is passed to the receiver > application is still ordered. We can imagine that a flow of > messages from a monitoring device could just need that. > > - "consecutive message ordering" (o2) a missing message is > not allowed in the delivered sequence. A message that cannot be > waited for any longer, should break the sequence, and subsequent > messages not be passed to the app (so this enforces passing only > consecutively ordered sequences). > > The spec seems to endorse either o1 (section 2.4) or o2 (section 3.3.2). > Instead, it should clearly define these two variants. > > *Definition 1*: (message ordering, o1 above): > When "message ordering" is required, an RMP implementation that is > required to do "message ordering" , MUST NOT make any two received > messages available to the application in a different order than their > sending order. > > *Definition 2*: (consecutive message ordering, o2 above): > When "consecutive message ordering" is required, an RMP implementation > MUST enforce "message ordering", and in addition MUST NOT make a > received message available to the application if its was sent after > another message that is not yet available to the application. > > Depending on which variant is used, o1 or o2, either one or the other of > the current options (b)and (a) respectively > in Rel 57 will apply. > The decision when to decide to "not wait anymore", remains to be decided > (TimeToLive of the first unordered message? The min of TimeToLives of > all unordered messages? Or a max unordered window size parameter, > related to Rel 56.) > > -------------------------------- meeting minutes 9.5: > > "...The text is currently unclear on whether sequenceNO other than 0 can > be used without ordering. The general consensus is no." > > *Issue*: restricting the use of sequence numbers to the message ordering > feature alone - and enforcing one message > per groupId otherwise, with seq nbr equal to 0 - will preclude > implementations from using of a whole set of fast and space-efficient > algorithms for duplicate elimination. > > *Proposal*: Do not preclude using sequence numbers for other purpose > than message ordering, at least until some conclusive results have been > obtained on testing duplicate elimination algorithms. The spec should > only require > > that (groupId + seq.nbr) be always unique. > If the concern is about how to instruct an RMP what to do when it sees a > sequence number in a message (should order? Should not?), that is > another problem that could be solved separately. > > If we resort to such tricks as using a different groupId for each > message that does not require ordering, this amounts to enforcing > duplicate check algorithms that are based on unique messageId strings. > This will lead to more costly duplicate check (less scalable and less > performant) and to the use of two different algorithms, if we still want > to use sequence number-based duplicate check for ordered sequence that > also need exactly once delivery. > -- SunNetwork 2003 Conference and Pavilion "An unparalleled event in network computing! Make the net work for you!" WHEN: September 16-18, 2003 WHERE: Moscone Center, San Francisco For more information or to register for the conference, please visit: http://www.sun.com/sunnetwork
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