Title: Re: [ebxml-msg] an assessment of the reliability of pulled messages
Jeff:
Your
Scenario #1 (Non-reliable Pull Request)
is not
realistic as you draft it, because you assume an RMP behavior that is quite
"new" w/r to WS-Reliability spec:
namely, that
the RMP will be able to resend the cached pulled message as a sync response of
an entirely new Pull request.
That would
assume that the RMP has some knowledge of the Pull semantics, and
knows somehow that all "Pulls" for this party ID are equivalent, so
that it can do the resending as a response of any of them.
The other
radical alternative for Non-reliable Pull Request that could
be taken (but which has many problems) can be summarized
as:
"Because it
is a Pull signal, we can redo it (MSH level) as many times as we want, when we
fail to get
a pulled
message. So no need to involve any RMP-level reliability."
Problems
are:
- that only
works if the Pull is idempotent, e.g. you need a flag saying "I want to re-pull
the same message as previous pull"
that
complicates things.
- some
caching is assumed on MSH side so that pulled messages are still available for
resending until they are acknowledged somehow. That seems to require a new
persistence mechansim at MSH level that would not be necessary if we rely just
on RMP presistence.
- that needs
be governed by an MSH-level Ack (which we precisely wanted to avoid
lately).
Trying to use
the "next" Pull as an Ack is very tricky: that assumes a complete serialization
of Pull+response pairs, which I think is very restrictive. We should allow for
implementations sending batches of Pull without waiting for the response between
each. That is quite possible when using concurrently several HTTP
connections, and even over a single HTTP connection
(pipelining).
- unless we
try to avoid situations where the same ebMS message can be successfully pulled
twice (whcih seems hard to guarantee) we'll need to do duplicate elimination at
MSH level (based on ebMS ID).
Jacques
-----Original Message-----
From: Jeff Turpin
[mailto:]
Sent: Wednesday, January 05,
2005 1:41 PM
To: Jacques Durand;
''
Subject: Re: [ebxml-msg] an
assessment of the reliability of pulled messages
Here are the
two proposals as I see them for a "reliable" pull transaction:
I.
Non-reliable Pull Request
----------
Step#1:
-Sender MSH: pass
Pull(PartyId) to
RMP.
-Sending RMP: send Pull(PartyId)
(non-reliable)
|
|
-Receiving RMP:
get the Pull (non-reliable)
-Receiver MSH: get the Pull, pass to
App
---------- Step
#2:
-Receiver MSH: gets the pull request and gets a waiting message
(response) from its queue, pass to RMP.
-Receiving RMP: send reliably the pulled
message over synch MEP
(SOAP
Response to the previous Pull, as this was a synchronous Pull) and persist this message (for possible
resend)
a.
failure
-Sending RMP: does not get the reliable
response, does not send an Ack
-Sender MSH: does not get a pulled
message.
-Sender MSH: schedules the next pull
request
|
|
-Receiver
RMP: RMP does not get the Ack for the reliable message (response), makes
message eligible
for
"resend" (makes
message available for next pull request)
b.
success
-Sender RMP: gets reliable response,
sends (callback) RMP Ack, passes "pulled" message to
MSH
-Sender MSH: Processes "pulled"
message
|
|
-
Receiver RMP: Receives Ack and notifies MSH of
Delivery
II. Reliable
Pull Request
----------
Step#1:
-Sender MSH: pass Pull(PartyId)
to RMP.
-Sending RMP: send Pull(PartyId)
(reliable)
|
|
-Receiving RMP:
get the Pull reliable request, pass to MSH
-Receiver MSH: get the Pull, pass to
App
---------- Step
#2:
-Receiver MSH: get the waiting message (response) from its queue,
pass to RMP.
-Receiving RMP: send reliably the pulled
message over synch MEP with bundled Ack
(SOAP
Response to the previous Pull, as this was a synchronous Pull) and persist this message (for possible
resend)
a.
failure
-Sending RMP: does not get the Ack, makes
request eligible for resend
-Sender MSH: does not get a pulled
message.
-Sender RMP: resends the same (duplicate RM
message ID) pull
request
|
|
-Receiver
RMP: RMP does not get the Ack for the reliable message (response), makes
message eligible
for
"resend" (makes
message available for next duplicate pull
request)
-Receiver RMP: Receives duplicate pull
request (duplicate RM message ID) and responds with the cached
reliable
pull message
(response)
b. success
-Sender RMP: gets
reliable response/Ack, sends (callback) RMP Ack, passes "pulled" message to
MSH
-Sender
MSH: Processes "pulled"
message
|
|
-
Receiver RMP: Receives Ack and notifies MSH of
Delivery
