VSAM buffers

IMS builds the VSAM buffer pool based on the number of buffers and the subpool sizes specified in the DFSVSMxx member of the IMS PROCLIB data set or, in batch or utility environments, in the DFSVSAMP data set.

You also can the use dynamic database buffer pools function to make changes to the number of buffers and the subpool sizes without bringing your IMS system offline.

Defining during system definition

When a DL/I call, such as an ISRT or GU, requires access to a VSAM data set, IMS makes VSAM PUT and GET calls as needed. The VSAM buffer pool is managed and manipulated by DFSMS, not by IMS.

Modifying dynamically

You can create new buffer pools and modify existing pools to be changed (or deleted) without having to bring your IMS system offline. While IMS resources are still actively in use, specify new VSAM shared resource pool definitions in the DFSDFxxx member of the IMS PROCLIB data set, and then issue the appropriate UPDATE POOL TYPE(DBAS) command.