Starting IMS systems and global command status

Global command status is the status of a shared IMS resource as set by online commands and as seen by all IMSplex members that have the resource defined.

If you are operating in an IMSplex environment that specifies PLEXPARM(GSTSTRAN(Y), GSTSDB(Y) or GSTSAREA(Y)), you must understand how the status of IMS resources as set by online commands is maintained at both the global and the local level, as well as how resource status is recognized by IMSplex members as individual IMS systems are started and stopped across the IMSplex.

For example, if the Resource Manager (RM) maintains global command status information for a database and the database is stopped by a command, all members of the IMSplex, whether they were running at the time the command was issued or not, see that the database is stopped. That same database can have a local status in an IMS system that is different than the global command status maintained in RM. Stopping a database globally while allowing access locally can be useful for preventing updates to the database from other IMSplex members while a local batch program processes the database.

RM maintains global command status for IMS resources by resource type. The maintenance of global command status is enabled for a resource type by specifying the PLEXPARM= parameter in the DFSDFxxx or DFSCGxxx PROCLIB member during IMS initialization.

You can assign global status to a resource dynamically by using one of the following commands:

• UPDATE IMS SET(PLEXPARM(GSTSDB(Y)) identifies that global database status is to be maintained on database commands.
• UPDATE IMS SET(PLEXPARM(GSTSAREA(Y)) identifies that global area status is to be maintained on area commands.
• UPDATE IMS SET(PLEXPARM(GSTSTRAN(Y)) identifies that global transaction status is to be maintained on transaction commands.

If global status is not explicitly specified for a resource type, RM does not maintain global status.

When RM maintains global status for a resource type, any commands issued against specific instances of the resource change the global status of the resource instance in RM. You can limit the affect of commands on the global status of a resources by using the SCOPE() parameter with the appropriate type-2 command:

• The SCOPE(ACTIVE) parameter limits the scope of commands to the active IMS systems that the command is routed to, and no global information is changed.
• The SCOPE(ALL) parameter specifies the scope of commands to the active IMS systems that the command is routed to and updates the RM status if applicable.

If a command is issued against a resource with global status before an IMS system is started, the starting IMS system can read the global status of resources in RM and apply them locally to the IMS system if the resources are valid.

The first IMS system to start in an IMSplex sets the PLEXPARM values that it knows about. IMS systems that start in the IMSplex subsequent to the first, use the PLEXPARM status definitions already in RM.

When an IMS system restarts and global status exists for the resource type in RM, the type of start determines which status takes precedence:

• For cold starts, the global status of databases, partitions, areas, and transactions takes precedence.
• For warm starts, the restarting IMS system first applies the local status saved in the log records and then applies the global status stored in RM only if it changed while the IMS system was down.

Before attempting to restart IMS again, complete one of the following actions:

1. Cancel IMS or shutdown IMS after restart completes. After the error condition reported in the DFS3308 message is fixed, restart IMS. IMS will be synchronized with RM status, and no additional action is required.
2. Allow the IMS restart to complete, then take the following actions:
   • Issue the appropriate UPDATE IMS SET(PLEXPARM) command to enable global status at this IMS.
   • Issue the appropriate QRY TRAN|DB|AREA SHOW(GLOBAL) commands to see the resources with global status.
   • Issue appropriate command with the SCOPE(ACTIVE) parameter to ensure that the IMS is synchronized with RM status.

RM stores global status information in its resource structure. If the resource structure should fail, RM repopulates the resource structure by having each active IMS system in the IMSplex update the resource structure with its local resources that have global status. Any global status for resources owned by an IMS system that is not active is not restored to the resource structure.