Designing a DEDB or MSDB buffer pool

Buffers needed to fulfill requests resulting 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 and FPBP64M 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. During emergency restart processing, the entire buffer pool can be briefly page-fixed. Consider the amount of available real storage when setting the DBBF value. IMS writes the total number of buffers to the X'5937' log.

For more information about page-fixing IMS resources, see IMS Version 15.3 System Administration.

DBFX

System buffer allocation.

This is a set of buffers that are page fixed during IMS initialization. The value should approximate the maximum number of buffers that are expected to be active in output thread processing at any one time. If the value is too small, dependent regions might have to wait for buffers.

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.