14 Replies Latest reply on Dec 11, 2013 5:21 AM by sebp

How to get the exception that caused a tx to rollback?

sebp Dec 9, 2013 9:31 AM

The com.arjuna.ats.internal.jta.resources.arjunacore.XAOnePhaseResource has the following commit method:

public int commit()
    {
        boolean doForget = false;

        try
        {
            // TODO we don't do an end here yet we do in 2PC. Check!!

            xaResource.commit(xid, true) ;
            return TwoPhaseOutcome.FINISH_OK ;
        }
        catch (final XAException xae)
        {
            if (jtaLogger.logger.isTraceEnabled()) {
                jtaLogger.logger.trace("XAOnePhaseResource.commit(" + xid + ") " + xae.getMessage());
            }

            switch (xae.errorCode)
            {
            case XAException.XA_HEURHAZ:
            case XAException.XA_HEURMIX:
                return TwoPhaseOutcome.HEURISTIC_HAZARD;
            case XAException.XA_HEURCOM:
                doForget = true;
                return TwoPhaseOutcome.FINISH_OK;
            case XAException.XA_HEURRB:
                doForget = true;
                return TwoPhaseOutcome.ONE_PHASE_ERROR;
            case XAException.XA_RBROLLBACK:
            case XAException.XA_RBCOMMFAIL:
            case XAException.XA_RBDEADLOCK:
            case XAException.XA_RBINTEGRITY:
            case XAException.XA_RBOTHER:
            case XAException.XA_RBPROTO:
            case XAException.XA_RBTIMEOUT:
            case XAException.XA_RBTRANSIENT:
            case XAException.XAER_RMERR:
                return TwoPhaseOutcome.ONE_PHASE_ERROR;
            case XAException.XAER_NOTA:
                return TwoPhaseOutcome.HEURISTIC_HAZARD; // something committed or rolled back without asking us!
            case XAException.XAER_INVAL: // resource manager failed, did it rollback?
                return TwoPhaseOutcome.HEURISTIC_HAZARD;
            case XAException.XA_RETRY:  // XA does not allow this to be thrown for 1PC!
            case XAException.XAER_PROTO:
                return TwoPhaseOutcome.ONE_PHASE_ERROR; // assume rollback
            case XAException.XAER_RMFAIL:
            default:
                return TwoPhaseOutcome.FINISH_ERROR;  // recovery should retry
            }
        }......

...

The XAException that is caught here contains the original error that caused the transaction to rollback. All this information is completely lost when commit returns only an error key. Even logging the error message does not help because the interesting exception is wrapped inside the XAException.

Any idea how I can get the original cause for the exception in my business logic? Btw. why does commit not simply throw another exception that wraps the original cause? Thanks in advance. Sebastian

1. Re: How to get the exception that caused a tx to rollback?

mmusgrov Dec 9, 2013 10:17 AM (in response to sebp)

Normally resources do their work in the before completion synchronization and report problems at that point and we remember the exception. Then in TransactionImple commit we report the problem if the transaction rolls back by setting the initCause of the rollbackException.

Please can you indicate your use case and be more explicit about which resource is causing problems.
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2. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 9, 2013 11:27 AM (in response to sebp)

I think you are using an old version of Narayana, later version dump the stack trace too:
narayana/ArjunaJTA/jta/classes/com/arjuna/ats/internal/jta/resources/arjunacore/XAOnePhaseResource.java at master · jbos…

We changed that in [JBTM-1171] improve XAResource preparefailed logging - JBoss Issue Tracker
1 of 1 people found this helpful
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3. Re: How to get the exception that caused a tx to rollback?

sebp Dec 10, 2013 2:39 AM (in response to mmusgrov)

I have a JEE application and I am trying to use the database for checking the constraints of my data model.When the tx finishes I want to catch any exceptions and translate them into my own exceptions that are known by the client. In the database I use deferred constraints to workaround some problems with Hibernate. The deferred constraints are checked by the database at the moment where the transaction commits and therefore a (postgresql) constraint violation exception is thrown up to OnePhaseResource.commit(). The commit method catches this exception and just returns an integer error code. The original cause is lost and it is not possible to give any useful hint about constraint violation to the client.
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4. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 10, 2013 5:36 AM (in response to sebp)

Hi Sebastian,

Did you see my comment above how that has been addressed since JBTM-1171?

Tom
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5. Re: How to get the exception that caused a tx to rollback?

sebp Dec 10, 2013 6:05 AM (in response to tomjenkinson)

Hi Tom,
yes I saw your comment and took a look into the new source of the commit method. The error is logged now and that helps a lot when we try to recover the error on the server side. You're right that [JBTM-1171] exactly describes my problem. But I wanted to point out that I'd like to catch the constraint violation exception to translate it and present something useful for the user. With the new changes in the commit method I still get the ONE_PHASE_ERROR in my catch clause. Is there any way to recover the original exception (besides crawling the logs)?
Regards Sebastian
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6. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 10, 2013 8:58 AM (in response to sebp)

Hi Sebastian,

I see what you mean now. Although we would possibly be able to add an initCause, the difficulty is that there could be several resources that we try to commit that may all report exceptions so I am not sure what the "API" would look like. What I mean is that we can have this scenario:

enlist 3 resources
tm::comit
commit resource 1
commit resource 2 -> SQL constraint violation 1
commit resource 3 -> SQL constraint violation 2

XAException.initCause contains which one?

If we can get a nice design for that I am happy to work with you on adding such a feature to the project.

Tom
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7. Re: How to get the exception that caused a tx to rollback?

sebp Dec 10, 2013 11:22 AM (in response to tomjenkinson)

Now I understand why the exception is not simply thrown. I will have a look at the JBTM code and maybe I'll have a nice design idea... Thanks so far
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8. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 10, 2013 11:39 AM (in response to sebp)

Great, thanks for that. Please do let us know if you find a solution you would like us to review.
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9. Re: How to get the exception that caused a tx to rollback?

jaikiran Dec 11, 2013 1:51 AM (in response to tomjenkinson)

Perhaps these Java 7 API will help:

http://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#addSuppressed%28java.lang.Throwable%29 (the JBTM code would add them as suppressed exceptions in the "one phase error" exception or whatever exception that gets thrown by JBTM)
http://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#getSuppressed%28%29 (the user code can then call this method on the exception that was thrown)
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10. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 11, 2013 2:44 AM (in response to jaikiran)

Hi Jaikiran,

That does look like a possible approach. Thanks for the heads up. Sebastian, do you fancy having a go at adding it? We are using JDK7 now in Narayana so its certainly an option available to us.

Here is the XAException: jboss-transaction-api_spec/src/main/java/javax/transaction/xa/XAException.java at master · tomjenkinson/jboss-transactio… as you can see, we don't disable the suppressed exception stuff so it should work.

The original XAEs from the resource managers would need passing around the core so its not an obvious change but it should be possible.

Tom
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11. Re: How to get the exception that caused a tx to rollback?

sebp Dec 11, 2013 3:13 AM (in response to tomjenkinson)

Using suppressed exceptions is a nice idea. But then the commit method would have to throw exceptions instead of returning error codes. I'll have a look at it. There are some other things to do before christmas but I'll report back asap.
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12. Re: How to get the exception that caused a tx to rollback?

tomjenkinson Dec 11, 2013 3:45 AM (in response to sebp)

Yeah, I don't think we should change the commit method signature. But there is a technique we use elsewhere (where Mike mentions about the deferred throwable in before completion) that we could try to apply:

narayana/ArjunaCore/arjuna/classes/com/arjuna/ats/arjuna/coordinator/TwoPhaseCoordinator.java at master · jbosstm/naraya…
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13. Re: How to get the exception that caused a tx to rollback?

marklittle Dec 11, 2013 5:20 AM (in response to tomjenkinson)

Yes, a big -1 to changing the signature of commit, rollback etc.
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14. Re: How to get the exception that caused a tx to rollback?

sebp Dec 11, 2013 5:21 AM (in response to marklittle)

Got it.
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