Tom Rutt wrote:
> I have one question inserted below.
>
> Tom Rutt
>
> Sunil Kunisetty wrote:
>
>> Here is the mail I sent on Duplicate Elimination a week ago.
>> It has the summary, possible solutions and my preferred solution.
>>
>> -----------------------------------------------------------------------------------------------------
>>
>> I'd like to summarize the options of using Duplicate Elimination for a
>> Request-Response MEP.
>>
>> 1) Cache the message until the original request expires and Send the
>> "payload response" for every subsequent request.
>> 2) Send an empty SOAP envelope.
>> (Note that when there is no AckRequested, there won't be any Ack
>> and
>> hence the SOAP envelope will have empty Header/body).
>> 3) Send a signal that it is a "Duplicate Message".
>> 4) Spec. says that this is combination is not supported.
>>
>> While I personally like (4), we can't do it as the TC voted to support
>> this combination.
>>
>> I'm very un-comfortable with (2) as it will cause all kinds of issues
>> and
>> as such it is meaningless/un-informative to send "empty signal".
>>
>> As per (1), while it is theoritcally reasonable and easy to implement,
>> it is impractical from a product/solution perspective.
>>
>> Here are few reasons:
>> (i) Potentially can throttle the server with memory being sucked up.
>> Generally speaking, expire time is used optimistically and will
>> have a
>> large life span. Caching responses that long is not too good .
>> (ii) I believe this thing (async. responses) is beyond the scope
>> of this specification and should be handled in the "OASIS
>> Asynchronous
>> Service Access Protocol TC" [1]
>> (iii) There are many subtle things about caching responses:
>> - there should be mechanism to invalidate the cache
>> - what if the request has time sensitive information. for ex.,
>> if I ask for getStockQuote for Oracle with a duration of
>> say 1 hr...
>> Assume the first message is lost.
>> Say the RMP resent the same message after 10 mins... they may
>> get a stock quote that was 10 mins. ago.
>> So if time sensitive data exists, there should be mechanism
>> for data resync..
>>
>> So for these reasons, I just like a RM signal [3] solution so that
>> the application can resend the request.
>>
>>
> The situation that causes the most trouble is when the response had
> been previously sent, so the responder RMP
> has no response payload to return since it did not invoke the second
> deliver. Thus the sender resending will
> not help all all.
>
> The reason to give an indication is so the sender will not continue to
> resend the duplicate, in cases where the original
Right. That's why I said I like to send a RM signal so that the Sender
can either resend the Message
with a different MessageId or query as you suggested.
Option 2 (sending an empty SOAP envelope) is the wrong thing to do.
> response is lost. However an indication will let the sender know it
> SHOULD NOT resend the duplicate. Instead, it
> could invoke other operations to query the server state (eg, get the
> current ballance of the account to see if the
> first invoke actually happened.
