Fast Path buffer allocation in DBCTL environments

IMS allocates Fast Path buffers because DEDB writes are deferred until after sync point processing.

The result of one 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 BMPs and CCTL threads until after the CI they contain is written back.

If you use the Fast Path 64-bit buffer manager, IMS manages the allocation of Fast Path buffers for you. The allocation of buffers is page fixed when the buffers are allocated.

If you do not use the Fast Path 64-bit buffer manager, you specify the number of buffers that IMS allocates by using the DBFX parameter. If the Fast Path buffer pool is defined exactly as the sum of all NBAs, BMPs and CCTL threads must wait for the buffers to come back to the global pool. BMPs and CCTL threads 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 or FPB request.