OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.

 


Help: OASIS Mailing Lists Help | MarkMail Help

ws-rx message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]


Subject: RE: [ws-rx] PR001 - Feedback on MSFT's MC proposal


Doug,

 

Thanks for the feedback. Detailed responses inline below.

 

The net is I don’t see anything below that can’t already be done using the proposal I made. As I already mentioned in the response to Anish’s message the only potential change to the proposal I made is adding a new EPR specifically for MC.

 

 

From: Doug Davis [mailto:dug@us.ibm.com]
Sent: Thursday, October 26, 2006 8:57 AM
To: ws-rx@lists.oasis-open.org
Subject: [ws-rx] PR001 - Feedback on MSFT's MC proposal

 


Per my todo, here's feedback on the MSFT proposal for PR001 which
also has the various use-cases interspersed.

MG: My understanding is that the AI you took was to provide a set of enumerated use cases so the two proposals could be compared. I do not believe that this mail does that. However, I’m willing to see the AI closed if you agree that you don’t have any additional use cases beyond this for MC.


Metacomments:
- Current solution in spec is not broken nor incompatible with WSA

 

MG: If this were true CR33 would not have been filed.


- This proposal will force a new PR review and Interop

 

MG: This is not a technical argument against the proposal. The TC always planned on a  second PR review and it’s up to the TC whether or not we really need another round of interop.


- This proposal does not address any new features or use-cases

 

MG: I agree. It fixes a part of the spec that did not work as designed. It also clearly describes the feature and what it is intended to. I see that as an improvement over the current spec.


Legend:
MC = MakeConnection
MP = MessagePending
CS = CreateSequence

Specific comments:
- Lack of support for multiple endpoints per Sequence.
  When a MC is received the receiver can determine which Sequence
  is being targeted by the ref-p's of the incoming message. However,
  not all messages being sent on that Sequence can be received by
  all anon endpoints.  How can the receiver of MC ensure that the
  proper message (e.g. response) is given to the proper anon endpoint?
  Ability to share RM state does not equate to share of messages.

 

MG: I think you are mixing two different scenarios here.

1) Support for using a single sequence to and from multiple endpoints. The proposal I made certainly supports this.

2) Support for querying a endpoint for specific messages. This is not needed to support 1, nor is it needed for any RM scenario. Which unreachable endpoint receives and processes a given message and when it does so are implementation problems in the Client RMD and part of its contract with the applications that use it.


- Restrictions on RM Processing model.
  Base specifications should, within reason, try to avoid restricting the
  usage pattens under which they are used.  Since the RM spec is silent on
  algorithm used to determine when (and how many) Sequences are used we need
  to be careful about adding things to the spec that would restrict the
  impl's choices.  Above we talk about a single Sequence spanning multiple
  endpoints, but going the other direction there may be RM processors that
  choose to group messages destined to the same endpoint under one Sequence.
  In essence what we're talking about grouping based on wsa:To.  This proposal
  would not allow for this type of processing model because all wsa:To values
  would be the WSA Anon URI.

 

MG: This is an implementation style argument and I don’t see a scenario here. However, this can be accomplished by the server returning a MP header with an appropriate EPR and the unreachable endpoint occasionally sending an empty MC to that EPR.


- How many MC messages are needed?
  This proposal would require one MC per Sequence. If there are multiple
  Sequences at play between the two endpoints the current spec allows
  for a single MC to pull back messages from any Sequence. This could be
  a significant performance issue.

 

MG:  Both proposals require one MC per Sequence. The only difference is that in this proposal one MC is for a specific Sequence; but the same number of messages are exchanged. There is not an issue here.


- Since MC is an optional feature, how does the receiver know it will be used?
  Here there are two reasons the receiver of the MC would like to know
  whether or not MC will be used at all. First, the receiver may choose to
  reject requests to use the anon EPR if MC will not be used - thus saving
  resources.  Second, in cases where RM is optional for messages targeted
  to the Anon EPR, if the receiver knows that MC will not be used it may
  choose to not turn on RM at all, thus allowing normal WSA rules to
  apply to its delivery.  This would still allow a non-MC enabled client
  to function, where if the receiving end assumed that MC were always
  an option it may never actually deliver any message until a MC is sent.
  Thus never sending any messages.

MG: The receiver can fault on receipt of MC if it wished to, so the first point above isn’t an issue. The second point does not have a clear use case. Why would an endpoint turn off RM if it knew MC wasn’t going to be used? That sounds like this is no longer an RM scenario. My proposal does not cover using MC for non-RM messages. I don’t understand how the current spec would address what you just described either.


  Also, if the receiver of the MC makes the wrong choice (meaning it thinks
  MC will not be used) and MC's do flow then a new (unused) Sequence will
  be created.

 

MG: If you are not expecting an MC why would you create a sequence instead of just faulting?


- Requires special AcksTo EPR construction.
  While obviously its possible to create AcksTo EPRs with distinguishing
  ref-p's, w/o this proposal there is no need to.  All RM protocol
  messages have a wsrm:Identifier already that is used to identify which
  Sequence is at play.  This would require a secondary mechanism to also
  be used.  While not a deal-breaker it is a duplication of function and
  forces exposure of the MC feature into the other RM aspects.  Current
  version has no impact the rest of the RM spec - thus when this RM
  feature is turned on it doesn't require a change to the rest of the RM
  stack.

MG: The current MC also has distinguishing information in it separate from the wsrm:Identifier. I do not see an issue here.


- The AcksTo is not the same thing as the RMS.
  Implicit in this proposal is that the AcksTo endpoint has access to all
  of the same information as the RMS - which is not necessarily true. The
  AcksTo EPR is not required to do anything more than be able to update the
  state of the RM Sequences w.r.t. Acks - nothing more.  This is one of the
  reasons we have a dedicated AcksTo EPR at all - otherwise we would have
  just overloaded an existing EPR - like wsa:ReplyTo or wsa:From. Using the
  AcksTo EPR for this purpose is forcing a certain implementation choice.

MG: There was a lot of discussion on last week’s call of sending protocol faults to the AcksTo EPR as they were protocol control messages. So this EPR is already overloaded. I think the MC is another type of protocol control message so I don’t see a problem here either. That said, I’m open to seeing a new MC EPR defined.


- Orphan AcksTo
  This proposal suggests that a MP header may contain an AcksTo EPR as a
  signal that the receiver of the MP should then send a MC to that EPR
  as a mechanism by which new Sequences can be created.  This would then
  create an 'orphan' AcksTo EPR.  This EPR is not associated with a
  Sequence, thus its an orphan, and quite a change to how RM works.
  Or if it is associated with a Sequence then what is the state of that
  Sequence?  This would imply that a Sequence is created before a CS is
  actually processed.

 

MG: Reusing the AcksTo EPR from the MP in the CS that flows back would solve this. I don’t really see an issue here either.


- MP on nonexistent message.
  This proposal talks about a MP being able to flow so that the sender of
  message can signal to the anon endpoint that a MC needs to be sent so a
  CS can flow.  But in cases where this is the first message being sent
  how can this work? There is no back-channel from the anon endpoint to
  send it on.  Also, even if there was some incoming message how did
  the sender of the MP who which anon endpoint sent it? There is no identifying
  info in the message to distinguish one endpoint from another.

MG: The unreachable endpoint can poll with empty MCs.

If the receiver of MCs receives an empty MC with no other identifying headers  (e.g. no previously communicated ref-params) then the sender of the MC is truly anonymous and the response to the MC will include a CS and information that will make the unreachable client identifiable in the future.  This is a non-issue.


- Poor performing CreateSequence
  When the sending endpoint needs to use MP to create new Sequence we see
  the following message exchanges:
  Client -> some msg           -> Server
  Client <- some msg+MP/AcksTo <- Server
  Client -> MakeConnection     -> Server/AcksTo
  Client <- CreateSequence     <- Server/AcksTo

  vs current solution:
  Client -> MakeConnection -> Server
  Client <- CreateSequence <- Server

MG: This is not correct. My proposal allows for polling for the CS with MC as well, so the minimal exchange in both cases is exactly the same. I see the first form above as a distinct advantage of my proposal over the current form in that it allows the server side to set an explicit relation between previously received messages and messages over a newly established sequence.


  As stated in the previous bullet, there's no guarantee that the "some msg"
  data is actually available to do that msg exchange, but also this
  proposed solution is quite a bit more verbose and non-optimized.

- Unreliable-in/Reliable-Out not supported.
  Client sends a GetQuote, ReplyTo=anon.  Server decides to use RM to
  send the response.  How can this work?  The proposal implies that
  either a CS or a MP is sent back but how and on what socket?

 

MG: No, the proposal is clear. It sends a MP on the backchannel triggering the client to respond with the MC to get the CS.


  Anon replyTo means the only thing that can flow back on the current
  sockets is the GetQuoteResponse so how does the CS flow?
  Anon doesn't allow the GetQuoteResponse to flow back on any other
  socket than the one carrying the request.  Some people argue that it
  can if we're in the error case (broken socket) and using RM, but what
  about the non-error case - socket is still there and waiting for a
  response?  WSA rules would still need to apply.  Or are we suggesting
  this proposal changes WSA processing rules?

 

MG: If this is a true req/resp WSDL then how does the current spec address this? That the server violate its own published contract at its whim? I would argue that if you are expecting a reliable response you need to establish the inbound sequence to handle it before you invoke that operation. There isn’t a good way to handle the error case otherwise.


- Places burden of creating new sequences on the wrong side.
  There are scenarios mentioned in this proposal where the RMD sends a
  MC to, in essence, ask for a CS to flow.  This is quite a change to
  the current RM processing model where its the RMS that is always in
  control over when to create new Sequence.  Also, this then leads to
  the question of how did the RMD know a new Sequence is needed?

 

MG: In both proposals you have to poll with MC.


- Client Identification
  Following on the previous comment, the proposal says:
    When an unreachable client requires a new inbound sequence it MAY
    send the MakeConnection header independently to RM service endpoint.
    Upon receipt of a MakeConnection header block that the RM Source
    cannot relate to an existing sequence it MUST respond with either
    a CreateSequence message on the protocol specific back channel
    of the request, or with a MakeConnectionRefused fault.
  How does the service know if a Sequence already exists? What unique
  info is there to compare?  

 

MG: If the MC previously returned identifying ref params it can identify the sender. There is not an issue here.

 

Since these MC's can be delayed in the
  network, its possible that many may be sent and thus lots of
  CreateSequences may flow - meaning lots of unused Sequences may be
  created.  See next point.

- Unnecessary Sequences/Message flows.
  Since we're talking about RM here we need to think about what happens
  in cases where messages are late to the party.  In this proposal if a
  rogue MC is received and the AcksTo EPR it pointed to is for a terminated
  Sequence then a CS will flow back.  This will cause an unused Sequence
  on both endpoints and cause the generation of unused MC's that will
  continually flow until the Sequence expires.  And worse, what if the
  CS had an Offer - we then double the number of unused Sequences.

 

MG: If the AcksTo is for a terminated seq then a fault can always be returned. This is an implementation detail.


- MP sent to unidentified client
  The proposal says that a MP can be sent on inbound traffic to the
  unreachable endpoint, but it doesn't link the MP header to the
  client or to the Sequence so how does the sender of the MP know
  whether or not any particular message can carry the MP header.

 

MG: The MP can be related to the sequence of the RM message it is piggy-backed on.


- MP & client id again
  The proposal says:
    In the circumstance where an RM Source wishes to initiate a sequence
    with an anonymous client, the RM Source MAY return a MessagePending
    header over an existing transport backchannel. The MessagePending
    header MAY contain an AcksTo EPR...
  How does the RMS know which anon client its talking to?

MG: The MP can be related to the sequence of the RM message it is piggy-backed on.


Misc:

Some pointers to old discussions:
Discussion if i089 at Raleigh f2f:
http://www.oasis-open.org/apps/org/workgroup/ws-rx/download.php/17492/MinutesWSRX-f2f-032306.html#_Toc131830356

Old proposal for i089 but the word doc contains a lot of the rationale
behind the thinking:
http://www.oasis-open.org/apps/org/workgroup/ws-rx/email/archives/200605/msg00123.html

Pointer to i010, which dealt with Sequences spanning multiple endpoints:
http://docs.oasis-open.org/ws-rx/issues/ReliableMessagingIssues.xml#i010

thanks
-Doug



[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]