Connections to the IMS control region

IMS makes one connection to its control region from each Db2 subsystem. IMS can make the connection either automatically or in response to a command.

Connections are made in the following ways:

• Automatically during IMS cold start initialization or at warm start of IMS if a Db2 connection was active when IMS is shut down.
• In response to the /START SUBSYS ssid command, where ssid is the Db2 subsystem identifier.

  The command causes the following message to be displayed at the logical terminal (LTERM):

  DFS058   START COMMAND COMPLETED

  The message is issued regardless of whether Db2 is active and does not imply that the connection is established.

The order of starting IMS and Db2 is not vital. If IMS is started first, when Db2 comes up, Db2 posts the control region MODIFY task, and IMS again tries to reconnect.

If Db2 is stopped by the STOP DB2 command, the /STOP SUBSYS command, or a Db2 abend, IMS cannot reconnect automatically. You must make the connection by using the /START SUBSYS command.

The following messages can be produced when IMS attempts to connect a Db2 subsystem. In each message, imsid is the IMS connection name.

• If Db2 is active, these messages are sent:
  • To the z/OS console:

    DFS3613I ESS TCB INITIALIZATION COMPLETE

  • To the IMS :

    DSNM001I IMS/TM imsid CONNECTED TO SUBSYSTEM ssnm

• If Db2 is not active, this message is sent to the IMS master terminal operator (MTO):

  DSNM003I IMS/TM imsid FAILED TO CONNECT TO SUBSYSTEM ssnm
           RC=00   imsid

  RC=00 means that a notify request has been queued. When Db2 starts, IMS is also notified.

  No message goes to the z/OS console.