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Subject: Re: [ws-tx] Issue 041 - WS-AT: Invalid events should not cause definedtransitions
Ram, comments interleaved. Alastair Ram Jeyaraman wrote: This is not the case. When Invalid State is returned to the other side it means "you communicated a protocol error: I have no idea what you and I are up to anymore. I cannot know how to proceed". This fault message indicates that my interlocutor is (or I am) non-conformant, bugged.Alastair, In the case of an InvalidState fault, the transaction outcome remains consistent. That is, if the transaction aborts, all the relevant parties abort. Example (among very many): Participant View state Preparing. Message received Commit. At this point I (one participant of what may be many) has received an outcome decision when I have not signalled Prepared to the Coordinator. This should never happen (bug). Now, the current table shows that the Participant should move to the Aborting state. We assume that means that the P should initiate rollback etc (subject of another issue). If it does, and rolls back, then there is no guarantee that the bugged coordinator will send Commit to all other participants. The Invalid State message conveys to the C the semantic that the P has aborted. But there is no guarantee that a bugged implementation will obey that: after all, it is bugged once, so why not twice?. The state of the overall transaction is completely indeterminate. This is not what is generally meant by a consistent outcome. As Peter pointed out in the issue statement, it is wrong to carry out any state transition at this point -- or at least, to any state other than We're Screwed. Another example: Coordinator View in state Preparing. Receives Committed. Sends message Invalid State. Goes into state Aborting. C has no idea what the P is really up to (it should never have sent the message Committed). If it assumes that the P has acted as if it had received Commit (which could only occur if the C was bugged), then it is now either going to commit the transaction as a whole (which shouldn't happen if another P rolled back), or it is going to abort the rest of the transaction (current, improperly expressed assumption), in which case the transaction is definitionally inconsistent: one (or more) Ps have committed, perhaps as a result of a C bug, all others have aborted. Of course, it should never assume that the first P has really committed, because if it (or the C itself) is bugged in one respect (sending Committed early, invalidly, or promoting such an early error, respectively) then either the P or the C may be bugged in any other respect. The transaction is, once again, in an indeterminate state. To communicate that a participant has reneged on its promise is to convey that the participant has acted heuristically. The charter prohibits this feature (heuristic reporting). I have never agreed with that (not that it's that big a deal), but that's how the author companies wanted it.In the case of InconsistentInternalState fault, the sending party has unilaterally reneged on its commitment to consistency; that is, the transaction outcome may be inconsistent across participants. I understand that there is some confusion around this phrase "participant cannot fulfill its obligations" used in the description of InconsistentInternalState fault. Perhaps rewording the description of InconsistentInternalState should express the meaning as intended: "This fault is sent by a participant to indicate a global consistency failure. This is an unrecoverable condition." -----Original Message----- From: Alastair Green [mailto:alastair.green@choreology.com] Sent: Friday, May 12, 2006 2:27 AM To: Mark Little Cc: Peter Furniss; Ram Jeyaraman; ws-tx@lists.oasis-open.org Subject: Re: [ws-tx] Issue 041 - WS-AT: Invalid events should not cause defined transitions I think it's pretty obvious that these two messages are intended for the same purpose (protocol error; non-conformant counterpart, all bets are off). I would like to see an explanation from the original author companies for this duplication, and a proper argument that it is not redundancy. Without that it seems very clear the AT message should go. I also agree that no state transition should follow a protocol error, i.e. the approach taken in Peter's sparse + text solution is correct. Sparse versus verbose is a stylistic question. Peter, I don't understand how a message like this could be used to respond to internal events. To whom would it be delivered? Alastair Mark Little wrote:+1 Peter Furniss wrote:I agree that distinguishing circumstances of faults is generally a good thing. Equally, one can also have too much of a good thing :-) But the problem with InconsistentInternalState is that the definitionin the text doesn't correspond with the use in the state table. Definition says its when the participant cannot fulfil its obligations. That presumably would be apply when a participant has gone prepared but now cannot obey the Commit or Rollback it receives (which sounds suspiciously like a heuristic warning which would be out of charter for this TC). But the use in the state tables is that Participant sends it when it receives contradictory messages from the coordinator - sending both Rollback and Commit (in either order). That would seem to be no different from any of the other InvalidState circumstances = "I am receiving messages that should not happen in the state I am now in - either you have sent a message you shouldn't have done or I've made astate transition I shouldn't have done". Receiving InvalidState should certainly cause an alert - but it's a pretty serious one, because someone isn't conformant - the parties aren't talking WS-AT any more. InconsistentInternalState could be used in other circumstances, aligned with its definition. It might even appear in the state table - perhaps as action triggered from an internal event (which currentlyappears as N/A, curiously) Peter------------------------------------------------------------------------*From:* Ram Jeyaraman [mailto:Ram.Jeyaraman@microsoft.com] *Sent:* 06 May 2006 01:42 *To:* ws-tx@lists.oasis-open.org *Subject:* RE: [ws-tx] Issue 041 - WS-AT: Invalid events should not cause defined transitions As a consumer of a fault, I would rather receive a more specific fault such as InconsistentInternalState, since it offer more specificinformation and helps distinguish from other possible error states. Specifically, upon receipt of an InconsistentInternalState fault, theconsumer may send an alert containing the specific cause, which is otherwise not possible, if it receives a more generic fault. Why should this fault be removed?------------------------------------------------------------------------*From:* Ram Jeyaraman [mailto:Ram.Jeyaraman@microsoft.com] *Sent:* Tuesday, March 28, 2006 10:25 AM *To:* ws-tx@lists.oasis-open.org *Subject:* [ws-tx] Issue 041 - WS-AT: Invalid events should not causedefined transitions This is identified as WS-TX issue 041. Please ensure follow-ups have a subject line starting "Issue 041 - WS-AT: Invalid events should not cause defined transitions".------------------------------------------------------------------------*From:* Peter Furniss [mailto:peter.furniss@erebor.co.uk] *Sent:* Monday, March 27, 2006 1:33 PM *To:* ws-tx@lists.oasis-open.org *Subject:* [ws-tx] New issue: WS-AT: Invalid events should not cause defined transitions Issue name -- WS-AT: Invalid events should not cause definedtransitionsPLEASE DO NOT REPLY TO THIS EMAIL OR START A DISCUSSISON THREAD UNTILTHE ISSUE IS ASSIGNED A NUMBER. The issues coordinators will notify the list when that has occurred. Target document and draft: Protocol: WS-AT Artifact: spec Draft: AT spec cd 1 Link to the document referenced:http://www.oasis-open.org/committees/download.php/17311/wstx-wscoor-1.1- spec-cd-01.pdfhttp://www.oasis-open.org/committees/download.php/17325/wstx-wsat-1.1-sp ec-cd-01.pdfSection and PDF line number: ws-at section 10, lines 503/505 coordinator table: Committed/Active, Committed/Preparing pariticipant table: Commit/Active, Commit/Preparing ws-at: seciton 6.1, line 371 Issue type: Design/Editorial Related issues: Issue Description: The receipt of a message when the receiver is in a state such that the event cannot occur between correct implementations should not cause a state transition and allow the transaction to complete "successfully". There is no need to distinguish "InvalidState" and "InconsistentInternalState". Issue Details Background InvalidState is defined in WS-Coordinator as being an unrecoverable condition, and in all the cases where it is a defined response in the WS-AT tables can only occur if one of the implementations is broken/bugged (apart than the volatile Prepared/None case, see separate issue). Providing a defined state transition, as if the circumstance were expected and could be recovered from is inappropriate. There can be no graceful completion of the protocol -it has gone fundamentally wrong. This does not preclude an implementation from attempting to tidy up and protecting its own resources, but there should be no required state transition for the implementation. The protocol exchange has gone off the map. The use of InconsistentInternalState to distinguish two cases where an invalid event occurs is unnecessary (and the definition in line 371 does not align with the use in the table - it is probably the coordinator that has been sending wrong messages). The use of InvalidState is appropriate in all cases. Proposed resolution The clearest solution would be to make invalid cells in the state tables empty, for the cells currently shown as InvalidState or InconsistentInternalState, and also for the N/A cells and explain this with text: "Where a cell is shown as empty - if the row is for an Inbound Event, an WS-C Invalid State faultshould be returned. The subsequent behaviour of the implementation isundefined. - if the row is for an Internal Event, event cannot occur in thisstate. A TM should view these occurences as serious internal consistency issues." Having invalid cells empty makes it significantly easier to read and check the state tables. It becomes much clearer that they are essentially "sparse" and the path through the table can be followed more easily. |
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