我在系统中遇到了不一致的事务回滚异常。它使用MaxDB v.7.8在JBoss v 4.0.2上运行。 MDB处理消息并调用一些更新实体bean属性的方法。我试图更改超时属性，但之前抛出异常。
有什么想法吗？
2015-04-28 01:05:14,053 [JMS SessionPool Worker-30] INFO ExchangeLog Got task termination payload for task 452312
2015-04-28 01:05:14,084 [JMS SessionPool Worker-30] INFO ExchangeLog Task 452312 terminated with status COMPLETED
2015-04-28 01:05:14,084 [JMS SessionPool Worker-30] INFO ExchangeLog MDG_EXPORT task (452312) succeeded.
2015-04-28 01:05:14,084 [JMS SessionPool Worker-30] INFO ExchangeLog find destination agent for EXPORT_ASSEMBLY
2015-04-28 01:05:14,084 [JMS SessionPool Worker-30] INFO ExchangeLog The destination agent for task EXPORT_ASSEMBLY is null
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog find destination agent for EXPORT_PART
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog The destination agent for task EXPORT_PART is null
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog find destination agent for RESOLVE_HIERARCHY
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog The destination agent for task RESOLVE_HIERARCHY is null
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog find destination agent for EXPORT_DRAWING
2015-04-28 01:05:14,099 [JMS SessionPool Worker-30] INFO ExchangeLog The destination agent for task EXPORT_DRAWING is null
2015-04-28 01:05:14,131 [JMS SessionPool Worker-30] ERROR ExchangeLog Error while task termination for task 452312. null; CausedByException is:
null
2015-04-28 01:05:14,146 [JMS SessionPool Worker-30] ERROR ExchangeLog Failed to remove task 452312 from database
javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:232)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:139)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.EntityContainer.internalInvoke(EntityContainer.java:514)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.local.BaseLocalProxyFactory.invoke(BaseLocalProxyFactory.java:413)
at org.jboss.ejb.plugins.local.EntityProxy.invoke(EntityProxy.java:50)
at com.sun.proxy.$Proxy292.setUserTimestamp(Unknown Source)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndUpdateEligibleWaitingTasks(TaskManager.java:362)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndRemoveTask(TaskManager.java:1062)
at com.proficiency.cg.core.mdb.task.TaskTerminationMDB.onCGMessage(TaskTerminationMDB.java:234)
at com.proficiency.cg.core.mdb.AbstractCgMDB.onMessage(AbstractCgMDB.java:75)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.jboss.invocation.Invocation.performCall(Invocation.java:345)
at org.jboss.ejb.MessageDrivenContainer$ContainerInterceptor.invoke(MessageDrivenContainer.java:475)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:185)
at org.jboss.ejb.plugins.MessageDrivenInstanceInterceptor.invoke(MessageDrivenInstanceInterceptor.java:87)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.RunAsSecurityInterceptor.invoke(RunAsSecurityInterceptor.java:94)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.MessageDrivenContainer.internalInvoke(MessageDrivenContainer.java:389)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker.invoke(JMSContainerInvoker.java:1090)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker$MessageListenerImpl.onMessage(JMSContainerInvoker.java:1392)
at org.jboss.jms.asf.StdServerSession.onMessage(StdServerSession.java:256)
at org.jboss.mq.SpyMessageConsumer.sessionConsumerProcessMessage(SpyMessageConsumer.java:904)
at org.jboss.mq.SpyMessageConsumer.addMessage(SpyMessageConsumer.java:160)
at org.jboss.mq.SpySession.run(SpySession.java:333)
at org.jboss.jms.asf.StdServerSession.run(StdServerSession.java:180)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:745)
java.lang.RuntimeException: Transaction marked for rollback, possibly a timeout
at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.doSchedule(QueuedPessimisticEJBLock.java:228)
at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.schedule(QueuedPessimisticEJBLock.java:183)
at org.jboss.ejb.plugins.EntityLockInterceptor.invoke(EntityLockInterceptor.java:85)
at org.jboss.ejb.plugins.EntityCreationInterceptor.invoke(EntityCreationInterceptor.java:53)
at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:48)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:139)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.EntityContainer.internalInvoke(EntityContainer.java:514)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.local.BaseLocalProxyFactory.invoke(BaseLocalProxyFactory.java:413)
at org.jboss.ejb.plugins.local.EntityProxy.invoke(EntityProxy.java:50)
at com.sun.proxy.$Proxy292.setUserTimestamp(Unknown Source)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndUpdateEligibleWaitingTasks(TaskManager.java:362)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndRemoveTask(TaskManager.java:1062)
at com.proficiency.cg.core.mdb.task.TaskTerminationMDB.onCGMessage(TaskTerminationMDB.java:234)
at com.proficiency.cg.core.mdb.AbstractCgMDB.onMessage(AbstractCgMDB.java:75)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.jboss.invocation.Invocation.performCall(Invocation.java:345)
at org.jboss.ejb.MessageDrivenContainer$ContainerInterceptor.invoke(MessageDrivenContainer.java:475)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:185)
at org.jboss.ejb.plugins.MessageDrivenInstanceInterceptor.invoke(MessageDrivenInstanceInterceptor.java:87)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.RunAsSecurityInterceptor.invoke(RunAsSecurityInterceptor.java:94)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.MessageDrivenContainer.internalInvoke(MessageDrivenContainer.java:389)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker.invoke(JMSContainerInvoker.java:1090)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker$MessageListenerImpl.onMessage(JMSContainerInvoker.java:1392)
at org.jboss.jms.asf.StdServerSession.onMessage(StdServerSession.java:256)
at org.jboss.mq.SpyMessageConsumer.sessionConsumerProcessMessage(SpyMessageConsumer.java:904)
at org.jboss.mq.SpyMessageConsumer.addMessage(SpyMessageConsumer.java:160)
at org.jboss.mq.SpySession.run(SpySession.java:333)
at org.jboss.jms.asf.StdServerSession.run(StdServerSession.java:180)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:745)
2015-04-28 01:05:14,146 [JMS SessionPool Worker-30] ERROR ExchangeLog Task termination for task 452312 failed.
Failed to remove task 452312 from database; nested exception is: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout, root cause: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout
javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:232)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:139)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.EntityContainer.internalInvoke(EntityContainer.java:514)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.local.BaseLocalProxyFactory.invoke(BaseLocalProxyFactory.java:413)
at org.jboss.ejb.plugins.local.EntityProxy.invoke(EntityProxy.java:50)
at com.sun.proxy.$Proxy292.setUserTimestamp(Unknown Source)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndUpdateEligibleWaitingTasks(TaskManager.java:362)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndRemoveTask(TaskManager.java:1062)
at com.proficiency.cg.core.mdb.task.TaskTerminationMDB.onCGMessage(TaskTerminationMDB.java:234)
at com.proficiency.cg.core.mdb.AbstractCgMDB.onMessage(AbstractCgMDB.java:75)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.jboss.invocation.Invocation.performCall(Invocation.java:345)
at org.jboss.ejb.MessageDrivenContainer$ContainerInterceptor.invoke(MessageDrivenContainer.java:475)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:185)
at org.jboss.ejb.plugins.MessageDrivenInstanceInterceptor.invoke(MessageDrivenInstanceInterceptor.java:87)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.RunAsSecurityInterceptor.invoke(RunAsSecurityInterceptor.java:94)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.MessageDrivenContainer.internalInvoke(MessageDrivenContainer.java:389)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker.invoke(JMSContainerInvoker.java:1090)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker$MessageListenerImpl.onMessage(JMSContainerInvoker.java:1392)
at org.jboss.jms.asf.StdServerSession.onMessage(StdServerSession.java:256)
at org.jboss.mq.SpyMessageConsumer.sessionConsumerProcessMessage(SpyMessageConsumer.java:904)
at org.jboss.mq.SpyMessageConsumer.addMessage(SpyMessageConsumer.java:160)
at org.jboss.mq.SpySession.run(SpySession.java:333)
at org.jboss.jms.asf.StdServerSession.run(StdServerSession.java:180)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:745)
java.lang.RuntimeException: Transaction marked for rollback, possibly a timeout
at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.doSchedule(QueuedPessimisticEJBLock.java:228)
at org.jboss.ejb.plugins.lock.QueuedPessimisticEJBLock.schedule(QueuedPessimisticEJBLock.java:183)
at org.jboss.ejb.plugins.EntityLockInterceptor.invoke(EntityLockInterceptor.java:85)
at org.jboss.ejb.plugins.EntityCreationInterceptor.invoke(EntityCreationInterceptor.java:53)
at org.jboss.ejb.plugins.CallValidationInterceptor.invoke(CallValidationInterceptor.java:48)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.SecurityInterceptor.invoke(SecurityInterceptor.java:139)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.EntityContainer.internalInvoke(EntityContainer.java:514)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.local.BaseLocalProxyFactory.invoke(BaseLocalProxyFactory.java:413)
at org.jboss.ejb.plugins.local.EntityProxy.invoke(EntityProxy.java:50)
at com.sun.proxy.$Proxy292.setUserTimestamp(Unknown Source)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndUpdateEligibleWaitingTasks(TaskManager.java:362)
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndRemoveTask(TaskManager.java:1062)
at com.proficiency.cg.core.mdb.task.TaskTerminationMDB.onCGMessage(TaskTerminationMDB.java:234)
at com.proficiency.cg.core.mdb.AbstractCgMDB.onMessage(AbstractCgMDB.java:75)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.jboss.invocation.Invocation.performCall(Invocation.java:345)
at org.jboss.ejb.MessageDrivenContainer$ContainerInterceptor.invoke(MessageDrivenContainer.java:475)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:185)
at org.jboss.ejb.plugins.MessageDrivenInstanceInterceptor.invoke(MessageDrivenInstanceInterceptor.java:87)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.RunAsSecurityInterceptor.invoke(RunAsSecurityInterceptor.java:94)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.MessageDrivenContainer.internalInvoke(MessageDrivenContainer.java:389)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker.invoke(JMSContainerInvoker.java:1090)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker$MessageListenerImpl.onMessage(JMSContainerInvoker.java:1392)
at org.jboss.jms.asf.StdServerSession.onMessage(StdServerSession.java:256)
at org.jboss.mq.SpyMessageConsumer.sessionConsumerProcessMessage(SpyMessageConsumer.java:904)
at org.jboss.mq.SpyMessageConsumer.addMessage(SpyMessageConsumer.java:160)
at org.jboss.mq.SpySession.run(SpySession.java:333)
at org.jboss.jms.asf.StdServerSession.run(StdServerSession.java:180)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:745)
Failed to remove task 452312 from database; nested exception is: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout, root cause: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout
at com.proficiency.cg.core.blc.task.TaskManager.releaseAndRemoveTask(TaskManager.java:1071)
at com.proficiency.cg.core.mdb.task.TaskTerminationMDB.onCGMessage(TaskTerminationMDB.java:234)
at com.proficiency.cg.core.mdb.AbstractCgMDB.onMessage(AbstractCgMDB.java:75)
at sun.reflect.GeneratedMethodAccessor142.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.jboss.invocation.Invocation.performCall(Invocation.java:345)
at org.jboss.ejb.MessageDrivenContainer$ContainerInterceptor.invoke(MessageDrivenContainer.java:475)
at org.jboss.resource.connectionmanager.CachedConnectionInterceptor.invoke(CachedConnectionInterceptor.java:185)
at org.jboss.ejb.plugins.MessageDrivenInstanceInterceptor.invoke(MessageDrivenInstanceInterceptor.java:87)
at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:105)
at org.jboss.ejb.plugins.TxInterceptorCMT.runWithTransactions(TxInterceptorCMT.java:335)
at org.jboss.ejb.plugins.TxInterceptorCMT.invoke(TxInterceptorCMT.java:166)
at org.jboss.ejb.plugins.RunAsSecurityInterceptor.invoke(RunAsSecurityInterceptor.java:94)
at org.jboss.ejb.plugins.LogInterceptor.invoke(LogInterceptor.java:192)
at org.jboss.ejb.plugins.ProxyFactoryFinderInterceptor.invoke(ProxyFactoryFinderInterceptor.java:122)
at org.jboss.ejb.MessageDrivenContainer.internalInvoke(MessageDrivenContainer.java:389)
at org.jboss.ejb.Container.invoke(Container.java:873)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker.invoke(JMSContainerInvoker.java:1090)
at org.jboss.ejb.plugins.jms.JMSContainerInvoker$MessageListenerImpl.onMessage(JMSContainerInvoker.java:1392)
at org.jboss.jms.asf.StdServerSession.onMessage(StdServerSession.java:256)
at org.jboss.mq.SpyMessageConsumer.sessionConsumerProcessMessage(SpyMessageConsumer.java:904)
at org.jboss.mq.SpyMessageConsumer.addMessage(SpyMessageConsumer.java:160)
at org.jboss.mq.SpySession.run(SpySession.java:333)
at org.jboss.jms.asf.StdServerSession.run(StdServerSession.java:180)
at EDU.oswego.cs.dl.util.concurrent.PooledExecutor$Worker.run(PooledExecutor.java:743)
at java.lang.Thread.run(Thread.java:745)
2015-04-28 01:05:14,146 [JMS SessionPool Worker-30] ERROR ExchangeLog Failed to process message: Task termination for task 452312 failed. ; nested exception is: Failed to remove task 452312 from database; nested exception is: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout, root cause: javax.ejb.TransactionRolledbackLocalException: Transaction marked for rollback, possibly a timeout; CausedByException is:
Transaction marked for rollback, possibly a timeout