Coupling XRC sessions through a cluster session

You can couple XRC sessions running in a logical partition to the same master session as a single entity. This single entity, or cluster session, gathers all coupled information for all XRC coupled sessions within a logical partition, and presents this information in the master data set as a single coupled session. The XQUERY command with the MASTER parameter indicates that the session is a cluster session.

You use the XRC PARMLIB parameter of ClusterMSession of the STARTUP category to indicate the master session name to which all XRC coupled sessions in a logical partition will be coupled. When a master session name is found in this parmlib parameter, every time the ANTAS000 address space is started or restarted, the ANTCLnnn address space is started to manage a cluster session for a logical partition. Then, each XRC session that is specified on an XCOUPLE command issued with the ADD parameter the system couples to this master session through this cluster session. All XRC coupled sessions in logical partition must be coupled through the cluster session.

The XRC PARMLIB parameter of ClusterName of the STARTUP category can be used to specify the name of the cluster session. If you do not specify this parameter, the default name is the system host name. The cluster session name is used to determine the name of the cluster data set that is required for a cluster session.

The cluster data set is used to determine the previous cluster session environment for a logical partition when the ANTCLnnn address space is being started or restarted. The information found in the cluster data set determines the behavior of a cluster session.

The following are rules guiding the use of a cluster session.

You can couple up to 13 XRC sessions in a logical partition through a cluster session. The first XRC session coupled through a cluster session causes the cluster session to be coupled to the master session. When the last session in a cluster session is uncoupled, the cluster session will be uncoupled from the master session.
You cannot issue XRC commands specifying an active cluster session name for the session_id.
The cluster session reflects to the master session the combined status of all XRC sessions coupled through the cluster session.
The system does not start a cluster session during startup of the ANTAS000 address space or through the MVS console command of F ANTAS000,CREFRESH if one of the following conditions exists:
- The previous master session used by the cluster is not the same as the master session specified in the ClusterMSession (including the name and hlq). XRC suspended or active sessions are currently coupled through this cluster session. XRC uses the cluster data set to make this determination.
- The cluster data set or the master data set cannot be located through normal catalog search, or either of these data sets cannot be read. The XRC PARMLIB parameter ClusterName might have been changed, or the cluster name specified on the CREFRESH command may be invalid.
- The cluster session is currently active on another logical partition. The SYSXRCLS enqueue for the mhlq.clustername was enqueued by another system in the complex.
- Storage cannot be obtained for the ANTCLnnn address space, or the address space failed to be created.
You can also issue XRC commands allowed for coupled sessions that are not in a cluster session to the XRC coupled sessions in a cluster session.
A cluster session will not be disabled during startup of the ANTAS000 address space or through the MVS console command of 'F ANTAS000,CREFRESH' if one of the following conditions exists (the cluster session will be enabled using the previous settings for the cluster session):
- The cluster session was previously enabled and one or more XRC sessions were coupled through the cluster session to a master session.
- The XRC PARMLIB parameter of ClusterMSession specifies a master session name that is different then the master session name that the cluster session was coupled to when the ANTCLnnn address space last terminated, and one or more XRC sessions were coupled through the cluster session.
A cluster session may be started/restarted using a different ClusterMSession value if no XRC sessions are currently coupled through the cluster session.
An XCOUPLE command specified with the ADD parameter will fail if one of the following conditions is true:
- The MSESSION value specified is different from the ClusterMSession value.
- 13 XRC sessions are already coupled through the cluster session.
- The master session has 14 coupled sessions.
- The ANTCLnnn address space is not active and the ClusterMSession indicates that a cluster session is to be used for the logical partition. This may be a transition situation or it may indicate that an error occurred attempting to create the ANTCLnnn address space.
- The cluster session encounters an error processing the request.

Note:

Functions described in this topic that can be performed for coupled sessions may also be performed for XRC sessions which are coupled through a cluster session. These functions cannot be performed using the cluster session name on the commands. You must issue the requests specifying the XRC sessions names, and the result will be provided to the master session through the cluster session.

In addition, any error that occurs for one or more XRC sessions that are coupled through a cluster session will cause the cluster session to indicate to the master session that the cluster session encountered an error. If different errors occurred, the XQUERY MASTER report may indicate the status of MIX. Issue the XSTATUS CLUSTER command to determine the status of each session.