Designing a DEDB buffer pool in the DBCTL environment

In a DBCTL environment, buffers needed to fulfill requests from database calls are obtained from a global pool called the Fast Path buffer pool.

If you are using the Fast Path 64-bit buffer manager, IMS creates and manages the Fast Path buffer pools for you and places DEDB buffers in 64-bit storage. When the Fast Path 64-bit buffer manager is enabled, you do not need to design DEDB or MSDB buffer pools or specify the DBBF, DBFX, and BSIZ parameters that define Fast Path buffer pools.

You can enable the Fast Path 64-bit buffer manager by specifying FPBP64=Y in the DFSDFxxx PROCLIB member. When the Fast Path 64-bit buffer manager is enabled, IMS ignores the DBBF, DBFX, and BSIZ parameters, if specified.

If you are not using the Fast Path 64-bit buffer manager, you must specify the characteristics of the pool yourself during IMS system definition and during IMS startup.

When specifying the characteristics yourself, three parameters characterize the Fast Path buffer pool:

DBBF

Total number of buffers.

The buffer pool is allocated at IMS startup in the ECSA or, if FPBUFF=LOCAL is specified in DFSFDRxx, in the FDBR private region. IMS writes the total number of buffers to the X'5937' log.

DBFX

System buffer allocation.

This is a set of buffers in the Fast Path buffer pool that is page fixed at startup of the first region with access to Fast Path resources.

BSIZ

Buffer size.

The size must be larger than or equal to the size of the largest CI of any DEDB to be processed. The buffer size can be up to 28 KB.