Re: [DISCUSSION] Async support for Saga
Thanks for sharing your thoughts, Willem. But I didn't really get your point. I read the code and found that compensation action works like this: 1. Alpha GrpcOmegaCallback send GrpcCompensateCommand to Omega 2. Omega CompensationMessageHandler handle the command, execute compensation logic and send TxCompensatedEvent to Alpha In this progress, Alpha doesn't wait for compensation success message after sending compensation command, it just returns. So the progress is already async. If what I said above is correct, please read the following, if not, please correct me. As to the current implementation, it's possible that compensation command is sent but no compensation success message received. I think what you said is Alpha should have a mechanism to handle compensation timeout, retry or just log it. But I think this an improvement should be done on the Alpha side. Am I right? In my opinion, to support async compensation, the only thing need to do is providing a way to let user code send TxCompensatedEvent. Sure I don't mean that we should expose the underly communication, GrpcSagaClientMessageSender for example, to user code. Providing a encapsulated interface will be better, just like what I mentioned before. Zheng Feng 于2019年7月23日周二 下午2:10写道： > > OK, I understand and with my prev experiences with the JTA and XA, it looks > similar with the XA.recovery() to get the in-doubt transactions. So the > omega side or the application have to keep the records of the pending > transactions, is it right ? > > Willem Jiang 于2019年7月22日周一 下午11:51写道： > > > Yes, We can kick off the recovery process or status verify process in > > Alpha if the distribute transaction is in suspend status, but in this > > case we need Alpha talk to customer Application to tell if we need to > > do the recovery again or just do some auditing there. It depends on > > the customer's configuration. > > > > Willem Jiang > > > > Twitter: willemjiang > > Weibo: 姜宁willem > > > > On Mon, Jul 22, 2019 at 11:38 PM Zheng Feng wrote: > > > > > > Hi Willem, > > > > > > In the term of providing some further processing extension, you mean that > > > the customer could help the state machine to recovery from the suspension > > > states ? > > > > > > Willem Jiang 于2019年7月22日周一 下午11:28写道： > > > > > > > If we provide the async compensation call, we need to do lots of thing > > > > on Alpha and Omega side. My suggestion we just use provide sync way to > > > > get the feedback of compensation immediately to keep the design > > > > simpler. > > > > > > > > As we are reimplementing the Alpha with state machine, there are some > > > > suspension state which could be caused by the timeout or the missing > > > > event message. > > > > I had a long talk with ZhangLei, we are agree that we could leave the > > > > status check or recovery to the customer by providing some further > > > > processing extension, as there are too many detail things in customer > > > > code to think about. > > > > > > > > Anyway, it's my pleasure to have this kind of discussion with the > > > > team, it's the beauty of Open Source project development, we are > > > > tackling the interesting problem by working together from different > > > > company :) > > > > > > > > Willem Jiang > > > > > > > > Twitter: willemjiang > > > > Weibo: 姜宁willem > > > > > > > > On Mon, Jul 22, 2019 at 5:14 PM Zheng Feng wrote: > > > > > > > > > > In term of the compensation method, I think I had discussed with > > Willem > > > > > before that it could introduce the @Status annotation for the alpha > > > > server > > > > > to query the compensation status. When the compensation method is > > async > > > > > which means it can not response immediately, it would return the > > > > > COMPENSATING result and the alpha server could query the @Status > > method > > > > to > > > > > check the compensation status, if this method returns COMPENSATE_OK, > > the > > > > > alpha server will mark the local transaction is compensated otherwise > > > > will > > > > > mark it with compensate_failed. > > > > > > > > > > Daniel Qian 于2019年7月21日周日 下午8:37写道： > > > > > > > > > > > I rethink the idea I proposed, yes, provide low level apis is a bad > > > > idea, > > > > > > and I also don't suggest that let user code use omega-xxx-transport > > > > api. > > > > > > > > > > > > I think the essential issues are three: > > > > > > > > > > > >1. How to pass tx context info across threads > > > > > >2. How to asynchronously tell Alpha that Saga is ended or > > aborted, > > > > which > > > > > >means not triggered on @SagaStart method returns. > > > > > >3. How to asynchronously tell Alpha that LocalTx is ended or > > > > aborted, > > > > > >which means not triggered on @Compensable method returns. > > > > > > > > > > > > I think we can keep using @SagaStart @Compensable for the > > > > XXXStartedEvent, > > > > > > and provide a helper to manually end/abort Saga/LocalTx. Thanks > > for PR > > > > #506 > > >
Re: [DISCUSSION] Async support for Saga
OK, I understand and with my prev experiences with the JTA and XA, it looks
similar with the XA.recovery() to get the in-doubt transactions. So the
omega side or the application have to keep the records of the pending
transactions, is it right ?
Willem Jiang 于2019年7月22日周一 下午11:51写道：
> Yes, We can kick off the recovery process or status verify process in
> Alpha if the distribute transaction is in suspend status, but in this
> case we need Alpha talk to customer Application to tell if we need to
> do the recovery again or just do some auditing there. It depends on
> the customer's configuration.
>
> Willem Jiang
>
> Twitter: willemjiang
> Weibo: 姜宁willem
>
> On Mon, Jul 22, 2019 at 11:38 PM Zheng Feng wrote:
> >
> > Hi Willem,
> >
> > In the term of providing some further processing extension, you mean that
> > the customer could help the state machine to recovery from the suspension
> > states ?
> >
> > Willem Jiang 于2019年7月22日周一 下午11:28写道：
> >
> > > If we provide the async compensation call, we need to do lots of thing
> > > on Alpha and Omega side. My suggestion we just use provide sync way to
> > > get the feedback of compensation immediately to keep the design
> > > simpler.
> > >
> > > As we are reimplementing the Alpha with state machine, there are some
> > > suspension state which could be caused by the timeout or the missing
> > > event message.
> > > I had a long talk with ZhangLei, we are agree that we could leave the
> > > status check or recovery to the customer by providing some further
> > > processing extension, as there are too many detail things in customer
> > > code to think about.
> > >
> > > Anyway, it's my pleasure to have this kind of discussion with the
> > > team, it's the beauty of Open Source project development, we are
> > > tackling the interesting problem by working together from different
> > > company :)
> > >
> > > Willem Jiang
> > >
> > > Twitter: willemjiang
> > > Weibo: 姜宁willem
> > >
> > > On Mon, Jul 22, 2019 at 5:14 PM Zheng Feng wrote:
> > > >
> > > > In term of the compensation method, I think I had discussed with
> Willem
> > > > before that it could introduce the @Status annotation for the alpha
> > > server
> > > > to query the compensation status. When the compensation method is
> async
> > > > which means it can not response immediately, it would return the
> > > > COMPENSATING result and the alpha server could query the @Status
> method
> > > to
> > > > check the compensation status, if this method returns COMPENSATE_OK,
> the
> > > > alpha server will mark the local transaction is compensated otherwise
> > > will
> > > > mark it with compensate_failed.
> > > >
> > > > Daniel Qian 于2019年7月21日周日 下午8:37写道：
> > > >
> > > > > I rethink the idea I proposed, yes, provide low level apis is a bad
> > > idea,
> > > > > and I also don't suggest that let user code use omega-xxx-transport
> > > api.
> > > > >
> > > > > I think the essential issues are three:
> > > > >
> > > > >1. How to pass tx context info across threads
> > > > >2. How to asynchronously tell Alpha that Saga is ended or
> aborted,
> > > which
> > > > >means not triggered on @SagaStart method returns.
> > > > >3. How to asynchronously tell Alpha that LocalTx is ended or
> > > aborted,
> > > > >which means not triggered on @Compensable method returns.
> > > > >
> > > > > I think we can keep using @SagaStart @Compensable for the
> > > XXXStartedEvent,
> > > > > and provide a helper to manually end/abort Saga/LocalTx. Thanks
> for PR
> > > #506
> > > > > (SCB-1385) we can use TransactionContext to achieve that. Below is
> a
> > > code
> > > > > sample:
> > > > >
> > > > >
> > > > > @SagaStart(async=true)
> > > > > public void foo() {
> > > > >TransactionContext txContext =
> OmegaContext.getTransactionContext();
> > > > >someAsyncCall()
> > > > > .onSuccess(Callback() {
> > > > > omega.endSaga(txContext);
> > > > > })
> > > > > .onException(Callback() {
> > > > > omega.abortSaga(txContext);
> > > > > })
> > > > > }
> > > > >
> > > > > @Compensable(async=true, compensationMethod="rollbackBar")
> > > > > public void bar() {
> > > > >TransactionContext txContext =
> OmegaContext.getTransactionContext();
> > > > >someAsyncCall()
> > > > > .onSuccess(Callback() {
> > > > > omega.endTx(txContext);
> > > > > })
> > > > > .onException(Callback() {
> > > > > omega.abortTx(txContext);
> > > > > })
> > > > > }
> > > > >
> > > > > The async attribute on @SagaStart and @Compensable prevents
> > > Saga/LocalTx
> > > > > ended when method returns.
> > > > > TransactionContext object can be passed around safely because it's
> > > > > immutable.
> > > > > What I have not considered clearly is that how to deal with
> > > compensation
> > > > > method if it's also async.
> > > > >
> > > > >
> > > > > Willem Jiang 于2019年7月20日周六 下午10:30写道：
> > > > > >
> > > > > > Yeah, I agree we need provide some low level API
