Overflow buffer allocation for BMPs

Overflow buffer allocation for BMPs is optional and is used for exceptional buffer requirements when the normal buffer allocation has been exhausted.

If you use the Fast Path 64-bit buffer manager, access to the overflow buffers is multi-threaded and multiple BMP regions and CCTL threads can use overflow buffers at the same time.

If you do not use the Fast Path 64-bit buffer manager, the access to the overflow buffers by a BMP region or CCTL thread is dependent on obtaining a latch that serializes all BMPs and CCTL threads currently in an overflow buffer state. If the latch is not available, the region has to wait until it is available. After the latch has been obtained, the NBA value is increased by the OBA value and normal processing resumes. The overflow buffer latch is released during sync point processing. At any point in time, only the largest OBA request among all the active BMPs and CCTL threads is page fixed in the Fast Path buffer pool.

The combined value of the NBA and OBA parameters specified for a dependent region define the maximum number of buffers that Fast Path can allocate to the region.