Connection concentrator required with WebSphere MQ Transaction Manager and DB2 for OS/390


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, 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 OS/390 servers: when using WebSphere MQ to coordinate distributed transactions involving DB2 for z/OS and DB2 for i5/OS 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.