How IMS dependent region connections work

The IMS attachment facility that is used in the control region is also loaded into dependent regions. A connection is made from each dependent region to Db2. This connection is used to pass SQL statements and to coordinate the commitment of Db2 and IMS work.

The following process is used by IMS to initialize and connect.

1. Read the SSM from IMS.PROCLIB.

   A subsystem member can be specified on the dependent region EXEC parameter. If it is not specified, the control region SSM is used. If the region is never to connect to Db2, specify a member with no entries to avoid loading the attachment facility.

2. Load the Db2 attachment facility from prefix.SDSNLOAD.

   For a batch message processing (BMP) program, the load is not done until the application issues its first SQL statement. At that time, IMS attempts to make the connection.

   For a message processing program (MPP) region or IMS Fast Path (IFP) region, the connection is made when the IMS region is initialized, and an IMS transaction is available for scheduling in that region.

   An IMS subsystem establishes the following connections to Db2:

   • A control region coordinator connection
   • An application connection from each dependent region

If Db2 is not active, or if resources are not available when the first SQL statement is issued from an application program, the action taken depends on the error option specified on the SSM user entry. The options are:

Option

Action

R

The appropriate return code is sent to the application, and the SQL code is returned.

Q

The application abends. This is a PSTOP transaction type; the input transaction is re-queued for processing, and new transactions are queued.

A

The application abends. This is a STOP transaction type; the input transaction is discarded, and new transactions are not queued.

The region error option can be overridden at the program level by using the resource translation table (RTT).