[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]
Subject: RE: [wsbpel-implement] Fault tolerance considerations
I’m only asserting two things: 1- The nature of BPEL makes it almost impossible to guarantee that the
path between a receive and a reply will happen in an amount of time that make
it usable as a synchronous operation. The time between the receive and the
reply may be very long, and a lot of stuff may happen during that time in both
ends of the connection. 2- It is a mistake for the BPEL specification to assume that a WSDL
request-response operation means synchronous operation, because a WSDL 1.1 request-response
operations can be implemented as synchronous or asynchronous, depending on the
binding. The end result is that when you do an invoke, you may be waiting for a
long time (maybe weeks), because you may invoke a non-BPEL web service that was
implemented asynchronously. Using the example given by Ron in the original message: <sequence> <receive name="rcv" ... /> <assign name="as1" ... /> <invoke name="inv" ... /> <assign name="as2" ... /> <reply name="rep" ... /> </sequence>
Let assume the invoke is calling a non-BPEL web service that uses a WSDL
request-response operation that was implemented asynchronous and takes 10 days
to respond. That means the time between receive and reply may take 10 days in
the best case scenario. Will you maintain that session open that time? -- Regards, Mike Marin -----Original
Message----- I don't fully
understand your proposal. Right now BPEL supports two modes of operation:
synchronous (receive/reply, in connection with a WSDL request/response
operation) and asynchronous (receive/invoke, in connection with two WSDL
one-way operations). So the choice is there. Why force everything to be
asynchronous? Ugo -----Original
Message----- Edwin’s suggestion does
make sense; but note that this is not only an “error recovery” issue. This
arises during normal operation. Let assume that your engine handle thousands of
processes per hour, and so at any given moment, some of those processes will be
in between the receive/reply pair. How do you bring the engine down for
maintenance (let say hardware upgrade or database backup)? The act of bringing the
engine down will certainly stop some of the processes in the middle of the
receive/reply pair. Most engines will consider shutting down the engine as a
normal operation, and they will keep the state of all the running processes,
but in this case you are forced into considering it as an abnormal operation
for those processes that are in the receive/reply pair. Again, IMHO receive/reply
should be asynchronous. They can be seen as synchronous from a invoke perspective,
but unless is implemented as asynchronous it creates unnecessary issues for the
implementer. -- Regards, Mike Marin -----Original
Message----- Tony, Dear
Ron, Mike, Ugo, and others, Is this
problem not occurring because of layer violation. Surely BPEL - and BPEL
implementations - should not need to worry beyond setting a timeout at the
sending side on an invoke to which a reply is expected. At the BPEL
should just a hand a message over to the SOAP HTTP implementation, and receive
messages back from it. Exactly how the message is sent (and in particular
whether the response rides on an HTTP response or request is surely not a BPEL
concern (???) I think the
issue arises only in error cases, where error recovery/handling may need some
extra insight into the lower-level binding characteristics. As Edwin has
suggested, this can be determined at deployment time, along with suitable
recovery policies. Obviously this sort of thing is implementation-specific, but
Edwin's approach makes a lot of sense. |
[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]