Connection concentrator required with WebSphere MQ Transaction Manager and Db2 for z/OS

When running applications in an IBM® WebSphere® MQ (formerly known as IBM MQSeries®) environment, WebSphere MQ can act as an XA-compliant transaction manager, coordinating any distributed, two-phase commit transactions. When WebSphere MQ is acting as a transaction manager in this way, and the data sources are from the Db2 family of products, there are several configuration requirements.

Most of the configuration requirements in such a transaction manager environment are already documented elsewhere. For example, you must set the Db2 configuration parameter tp_mon_name to MQ at the Db2 runtime client.

However, there is a configuration requirement that was missing. The requirement is specific to Db2 Connect when connecting to data sources that are Db2 for z/OS servers: when using WebSphere MQ to coordinate distributed transactions involving Db2 for z/OS and IBM Db2 for IBM i servers, the Db2 Connect connection concentrator feature must be enabled at the gateway. The connection concentrator is enabled when the value of the max_connections configuration parameter is greater than the value of the max_coordagents configuration parameter.

If you do not enable the connection concentrator, unexpected transaction behavior will result.

If you are using the WebSphere MQ Transaction Manager and Db2 for z/OS server, the application must set the special registers for each local or global transaction.