Retrying transactions

I got an error part way through the transaction, e.g. a deadlock, transaction timeout,

something I called did

setRollbackOnly()

or threw a system exception.

How do I recover from this?

Handling the exception

You should let the exception propogate out past the transaction boundary.

e.g. If you have a stateless session bean that starts the transaction you rethrow

the error to it and let it rethrow to the caller.

The transaction is dead, nothing you can do inside the transaction will let you fix it.

Retrying

JBoss has a feature that lets you check exceptions to see whether they are retryable.

You just write some code to examine the exception, example from the testsuite:

/*
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package org.jboss.test.retry.interfaces;

import javax.ejb.*;
import java.rmi.*;


public class RetryHandler implements org.jboss.ejb.plugins.TxRetryExceptionHandler
{
   public boolean retry(Exception ex)
   {
      System.out.println("**** testing retry ****");
      if (ex instanceof RetryException)
      {
         RetryException.wasRetried = true;
         return true;
      }
      return false;
   }
}

This is configured in

META-INF/[standard-]jboss.xml

against the transaction demarcation interceptor.

      <container-configuration extends="Standard Stateless SessionBean">
         <container-name>Retry</container-name>
         <container-interceptors>
            <interceptor>org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor</interceptor>
            <interceptor>org.jboss.ejb.plugins.LogInterceptor</interceptor>
            <interceptor>org.jboss.ejb.plugins.SecurityInterceptor</interceptor>
            <!-- CMT -->
            <interceptor transaction="Container">org.jboss.ejb.plugins.TxInterceptorCMT
               <retry-handlers>
                  <handler>org.jboss.test.retry.interfaces.RetryHandler</handler>
               </retry-handlers>
            </interceptor>
etc.

Usage

This retry will only work when this is the EJB that started the transaction.

i.e. It will not try to handle errors if this is just a

REQUIRED

ejb taking part in a transaction started by somebody else.

MDB

You don't use this method for

REQUIRED

mdbs. When the transaction fails, the message is NACKed back to the JMS provider which will then redeliver the message in a new transaction.

Be careful

• You don't want to continuously retry a transaction that will always fail

• You don't want to retry transactions when the error should be propogated back to the client, i.e. only it knows how to recover from the error/problem.

Referenced by: