Adding databases dynamically to an online IMS system

The function of the CREATE DB command corresponds to the function of the DATABASE system definition macro. Both declare databases to an online IMS system by creating a database directory (DDIR) control block in the IMS control region.

The CREATE DB command defines all of the database attributes that can be defined by using the DATABASE system definition macro. The attributes include:

• The recognition of the database by the online IMS system
• The access type
• The resident status of the database

You can issue the CREATE DB command either before or after you define the DBD, PSB, and ACBs for the database; however, if you issue the CREATE DB command after the ACBGEN process, IMS can take additional action based on the type of database defined.

If the ACBGEN process is complete and the DMB for the database is in the ACB library, IMS performs the following additional actions when the CREATE DB command is issued:

• For full-function databases, IMS loads the DMB for the database into the DMB pool at first schedule and if the resident option is selected, IMS makes the DMB for the database resident at the next restart of IMS.
• For DEDB databases, IMS chains the DMB into the DEDB DMCB chain.

  IMS also checks to see if the CI size for any area in the DMCB is larger than the size defined for the Fast Path global buffer pool. If a CI size is too large, the CREATE DB command fails with condition code E3.

  Also, if any DEDB area name already exists in the Fast Path area list (FPAL), the CREATE DB command fails with condition code E4.

If a DMB for the database is not already in the ACB library when a CREATE DB command is issued, IMS still adds the database to the online system, but the database has a status of NOTINIT. Before the database can be used, a DMB for the database must be added to ACB library and started. Unless you are adding an MSDB database, you can use the online change function for ACB library members to add the DMB.