Overflow buffer allocation (OBA)

The overflow buffer allocation (OBA) is optional and is used for exceptional buffer requirements when the normal buffer allocation (NBA) has been exhausted.

If you use the Fast Path 64-bit buffer manager, access to the overflow buffers is multi-threaded and multiple regions 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 region is dependent on obtaining a latch that serializes all regions 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 regions is page fixed in the Fast Path buffer pool.

When the Fast Path 64-bit buffer manager is used, the combined value of the NBA and OBA parameters specified for a dependent region define the maximum number of buffers that the Fast Path 64-bit buffer manager can allocate to that region.