Fast Path buffer allocation when the DBFX parameter is used

From the total number of Fast Path buffers specified by the DBBF parameter, IMS set asides a number of the buffers to use for DEDB writes. The number of buffers that IMS sets aside is specified by the DBFX parameter.

The result of one transaction or sync interval is written back by one output thread. These output threads run from the control region in SRB mode. Buffers allocated to an output thread are therefore not available to dependent regions until after the CI they contain is written back.

If the Fast Path buffer pool is defined exactly as the sum of all NBAs, dependent regions must wait for the buffers to come back to the global pool. Fast Path regions can process the next transaction as soon as the sync point completes. Sync point processing does not wait for the output thread to complete. The allocation of buffers is page fixed at the start of the first region specifying an NBA request.

If you use the Fast Path 64-bit buffer manager, IMS manages the Fast Path buffers for you and you do not specify need to specify the DBFX, DBBF, or BSIZ parameters. The allocation of buffers is page fixed when the buffers are allocated.