Resource Health Monitoring Java EE Connector Architecture Resource Adapter

11-8 Programming JTA for Oracle WebLogic Server The WebLogic Server transaction manager then continues to retry commit of the XAResources for these transactions. As discussed in Section 11.2, Registering an XAResource to Participate in Transactions , one purpose of the WebLogic Server transaction manager resource registration API is for bootstrapping XAResource instances for recovery. You must ensure that an XAResource instance is registered with the WebLogic Server transaction manager upon server restart. The WebLogic Server transaction manager retries the commit call every minute, until a valid XAResource instance is registered with the WebLogic Server transaction manager. When a transaction manager that is acting as a transaction coordinator crashes, it is possible that the coordinator may not have logged some in-doubt transactions in the coordinators transaction log. Thus, upon server restart, the coordinator must call XAResource.recover on the resource managers, and roll back the in-doubt transactions that were not logged. As with commit retries, the WebLogic Server transaction manager retries XAResource.recover every 5 minutes, until a valid XAResource instance is registered with the WebLogic Server transaction manager. The WebLogic Server transaction manager checkpoints a new XAResource in its transaction log records when the XAResource is first enlisted with the WebLogic Server transaction manager. Upon server restart, the WebLogic Server transaction manager then calls XAResource.recover on all the resources previously checkpointed removed from the transaction log records after the transaction completed. A resource is only removed from a checkpoint record if it has not been accessed for the last PurgeResourceFromCheckpointIntervalSeconds interval default is 24 hours. Therefore, to reduce the resource recovery overhead, you should ensure that only a small number of resource manager instances are registered with the WebLogic Server transaction manager. When implementing XAResource.recover, you should use the flags as described in the XOpen XA specification as follows: ■ When the WebLogic Server transaction manager calls XAResource.recover with TMSTARTRSCAN, the resource returns the first batch of in-doubt Xids. The WebLogic Server transaction manager then calls XAResource.recover with TMNOFLAGS repeatedly, until the resource returns either null or a zero-length array to signal that there are no more Xids to recover. If the resource has returned all the Xids in the previous XAResource.recoverTMSTARTRSCAN call, then it can either return null or a zero-length array here, or it may also throw XAER_ PROTO , to indicate that it has finished and forgotten the previous recovery scan. A common XAResource.recover implementation problem is ignoring the flags or always returning the same set of Xids on XAResource.recoverTMNOFLAGS. This causes the WebLogic Server transaction manager recovery to loop infinitely, and subsequently fail. ■ The WebLogic Server transaction manager XAResource.recover with TMENDRSCAN flag to end the recovery scan. The resource may return additional Xids.

11.6 Resource Health Monitoring

To prevent losing server threads to faulty XAResources, WebLogic Server JTA has an internal resource health monitoring mechanism. A resource is considered active if either there are no pending requests or the result from any of the XAResource pending requests is not XAER_RMFAIL. If an XAResource is not active within two minutes, the WebLogic Server transaction manager declares it dead. Any further requests to the XAResource are shunned, and an XAER_RMFAIL XAException is thrown. Coordinating XAResources with the WebLogic Server Transaction Manager 11-9 The two minute interval can be configured using the maxXACallMillis JTAMBean attribute. It is not exposed through the Administration Console. You can configure maxXACallMillis in the config.xml file. For example: Domain .... JTA MaxXACallMillis=240000 .... Domain To receive notification from the WebLogic Server transaction manager and to inform the WebLogic Server transaction manager whether it is indeed dead when the resource is about to be declared dead, you can implement weblogic.transaction.XAResource which extends javax.transaction.xa.XAResource and register it with the transaction manager. The transaction manager calls the detectUnavailable method of the XAResource when it is about to declare it unavailable. If the XAResource returns true , then it is not declared unavailable. If the XAResource is indeed unavailable, it can use this opportunity to perform cleanup and re-registration with the transaction manager. For more information, see weblogic.transaction.XAResource in the Oracle WebLogic Server API Reference.

11.7 Java EE Connector Architecture Resource Adapter

Besides registering with the WebLogic Server transaction manager directly, you can also implement the Java EE Connector Architecture resource adapter interfaces. When you deploy the resource adapter, the WebLogic Server Java EE container registers the resource managers XAResource with the WebLogic Server transaction manager automatically. For more information, see Programming Resource Adapters for Oracle WebLogic Server.

11.8 Implementation Tips