Hi Rajith,
See my commments inline.
On 9/4/07, Rajith Attapattu <[EMAIL PROTECTED]> wrote:
>
>
>
> Sorry if I was not clear enough. When I said session per service, I meant
> session per service instance (where it make sense). So no need to serialize
> access.
> Ex. If you have a service with scope='soap-session' and there are two
> clients talking to it, then you would have two instances of the service and
> would be using two JMS sessions (or two XA sessions). So each web service
> instance can run transactions independently of the other.
>
Ok, I think we are on same page.
> In the use case where services with scope='request' sharing sessions
> underneath, a given JMS session will only be used by one and only one
> service instance at a given time. (This will be tricky to implement, and
> only be worth if there is a high traffic scenario).
>
> Going direct, we still have a problem with receving messages. As far I
> > know, it is not possible to do a JTA receive using the async MessageListener
> > interface. One would need to either poll, or use the MessageConsumer
> > interfaces.
>
>
> Async or sync message receive is orthogonal to the transactions. Can you
> elaborate a bit more
>
Sure... When receiving messages when not using JTA, you can simply set up a
MessageListener via the MessageConsumer (as is the current practice in
AXIS). In the JTA case there is the compilication that the JTA transaction
needs to be started before the message is consumed. So you can do something
like this (ugly):
jta.begin();
session.receive(timeout);
if (timeout)
jta.rollback();
else
do some stuff...
jta.commit();
Alternatively you can use the ConnectionConsumer / ServerSessionPool
interfaces which allow one to start a JTA tx before the message is actually
consumed. This is a bit complicated, and also is an "optional" feature.
Or you can use MessageConsumer and try to enroll the XASession in the
transaction from the MessageListener.onMessage method. I do not believe this
to be entirely legal as far as the spec is concerned, but I hear it works on
some JMS providers.
In either case there is the issue of who begins and commits the JTA
> > transaction (AXIS2 or the service), and if its the service, it is not clear
> > how that interaction would look.
> >
> I'm more inclined toward an MDB-like model, where AXIS starts the TX,
> > calls the service, and then barring some indication to the contrary,
> > attempts to commit.
>
>
> IMO Axis2 should not commit or rollback automatically. Commits or
> rollbacks can happen based on business decisions as well as system errors.
> And in the case of a distributed transaction the decision to commit or
> rollback will come from the distributed transaction manager.
>
I agree in principle, but to do that, what you'd really need is to decouple
the notification that a message is available, from the act of consuming the
message.Something along these lines:
MyAxisService.onMessageReceived () {
jta.begin();
MessageContext ctx = consumeMessage() // message is consumed in the JTA
TX
this.doServiceWork();
jta.commit();
}
Getting something like that may be difficult (per my previous comments
regarding JTA / session enrollment).
-maciej
If there are any system(axis2) hiccups then axis2 will/should always throw a
> fault and the service author will be notified instead of axis2 doing
> rollback.
> In the case of a local transaction the service author may rollback and in
> a distributed transaction the XA resource (XA Session) will throw an
> exception in the prepare method and the the transaction manager will call
> rollback.
>
> -mbs
> >
> > On 9/4/07, Rajith Attapattu <[EMAIL PROTECTED]> wrote:
> > >
> > > Maciej,
> > >
> > > Currently there are a few problems with doing this. Lets identify the
> > > issues
> > > a) We create a new connection for each invocation (sending messages)
> > > b) Hence we create a new session for each invocation.
> > > c) When creating a session for receiving as well as sending transacted
> > > is set to true - no way to configure this.
> > > d) We currently don't expose the session outside for both transport
> > > sender/receiver, hence you cannot call commit or rollback on it.
> > > e) Since u are using JTA I assume it's a distributed transaction. So
> > > we need to create an XASession instead of a normal session.
> > >
> > > This can be done and here are some ideas. I spoke with Asankha briefly
> > > on this topic once.
> > >
> > > a) Asankha pointed out a new connection is created for each invocation
> > > as each service could have different connection params. (different
> > > provider,
> > > username,..etc)
> > > The downside of this is that creating new connections is an expensive
> > > operation. Especially if the same service sends frequent messages it will
> > > keep recreating connections. We should make this behaviour configurable.
> > > I would like if we could reuse connections where we can. Also in most
> > > cases a deployment would use a single provider and we can definitely
> > > optimize for this case.
> > > For this case we can get away with a single connection per axis2
> > > instance and session per service (one for sending and one for listening).
> > >
> > > If we can name connections then we could reuse them when defining
> > > services. This way we can check if an existing connection by that name
> > > exists and reuse it, if not create one.
> > >
> > > When we reuse connections there will be keep alive issues. Most
> > > providers have convenient and cheap ways of sending ping/pongs to keep the
> > > connection alive.
> > > So in a case where the service sends messages frequently this will
> > > help. If the service sends messages rarely and the cost of keep alive is
> > > greater than the occasional connection creation then the user can disable
> > > the reuse option.
> > >
> > > b) Creating a new session for each invocation is not optimal. Since
> > > the context hierarchy determines the scope of services and is independent
> > > of
> > > the transport session it's ok to reuse a JMS session underneath where ever
> > > it makes sense. If we introduce some thing similar to
> > > scope="transport-session" in HTTP for JMS, then we can allow users to
> > > directly use the underlying JMS transport similar to the way HTTP session
> > > is
> > > used.
> > >
> > > c) We can make the transacted property configurable. By default it
> > > will be false.
> > > <http://?auth=DQAAAHcAAABRNsIxA9tiVL3uczzey-x8FmU4gCUONPWKQAnlvhxhlFsCgDWBe2vo5cADP4RK1n0C-wf599ttpb3KuVGEQ1juQ4qqo7J7q47y0qAH12dW5DBAfbWjNSE-kzSN7uva1VddYFgwsvDPJHEKd2xLegIlVRPoMUsCpGd8rccaRUkjtg&shva=1>
> > > Ex: <parameter name="transport.jms.SessionTransacted">true</parameter>
> > >
> > > d) We need to expose the JMS session. Can we put the JMS session
> > > somewhere in the context hierarchy?
> > > I also see a getSessionContext in TransportListener interface, However
> > > SessionContext is written with HTTP in mind and is not generic enough.
> > > If we put it in the content hierarchy then the service author can
> > > retrieve it and call commit, rollback etc.
> > >
> > > e) We can create an XASession instead of a normal session based on
> > > configuration, provided the JMS provider supports it.
> > > Ex. <parameter name="transport.jms.XASession">true</parameter>
> > >
> > > Comments are very much appreciated.
> > >
> > > Regards,
> > >
> > > Rajith
> > >
> > > On 9/4/07, Maciej Szefler <[EMAIL PROTECTED]> wrote:
> > > >
> > > > Hi,
> > > >
> > > > I've been unable to find anything on the topic in Nabble, so I
> > > > thought I'd ping you all, and Asankha in particular regarding
> > > > transactions
> > > > in the JMS transport implementation.
> > > > In ODE we'd like to be able to consume/send messages through AXIS'
> > > > JMS transport. That in itself is not a problem. However, we'd like the
> > > > send/receive to be in enrolled in a JTA transaction. Any pointers on how
> > > > this can be done?
> > > >
> > > > -Maciej
> > > >
> > >
> > >
> >
>
