Overview of dynamic database buffer pools

You can dynamically reconfigure OSAM subpools and VSAM shared resource pools without taking your IMS system offline.

The dynamic database buffer pools function provides an alternative to specifying the OSAM and VSAM subpool definitions by changing the DFSVSMxx member of the IMS PROCLIB data set. DFSVSMxx is only processed during IMS initialization and the subpool definitions cannot be changed dynamically while IMS is online.

The dynamic database buffer pools function provides the ability to quiesce all activities against a subpool to make subpool definition changes dynamically by using the UPDATE POOL command. This command initiates the buffer pool reconfiguration that is defined in the DFSDFxxx member of the IMS PROCLIB data set while IMS resources are still actively in use.

In a single DFSDFxxx member, you can specify multiple unique OSAMxxx or VSAMxxx sections that contain different sets of definitions. When you invoke the UPDATE POOL command, specify the particular OSAMxxx or VSAMxxx section from which to take the updated definitions.

The dynamic changes are retained across an emergency restart because they are stored in the restart data set (RDS). However, the changes are lost with a subsequent cold or warm start. To make the changes permanent, it is necessary to make the changes in the DFSVSMxx member.

After you run the UPDATE POOL command, you can invoke the QUERY POOL command to return statistics for the current buffer pools and to confirm that the updated definitions are implemented as intended.

Types of supported buffer pool definition updates

You can make the following types of changes to your buffer pool definitions:

  • Change the number of buffers for an existing OSAM subpool
  • Create an OSAM subpool with a new subpool ID
  • Add a new set of buffers to an existing OSAM subpool
  • Delete an OSAM subpool
  • Change the number of buffers for an existing VSAM subpool
  • Create a subpool for an existing VSAM shared resource pool
  • Delete a subpool from an existing VSAM shared resource pool
  • Change the size of the buffers in a VSAM subpool
  • Create a VSAM shared resource pool