The DBFX value and the low activity environment

If the IMS or Fast Path activity in the system is relatively low, log buffers are written less often, and therefore output threads are scheduled or dispatched less frequently. This situation is likely to result in many buffers waiting to be written and therefore could cause wait-for-buffer conditions.

To alleviate or avoid wait-for-buffer conditions you can enable the Fast Path 64-bit buffer manager, which manages Fast Path buffers for you dynamically. When the Fast Path 64-bit buffer manager is enabled, IMS tracks buffer usage, adds or removes buffers as needed, and ignores the DBBF, DBFX, and BSIZ parameters, if they are specified.

If you are not using the Fast Path 64-bit buffer manager, specify a larger DBFX value.

When the Fast Path 64-bit buffer manager is not used, a special case to be considered is the BMP region loading or processing a DEDB and being the only activity in the system. For example, assume an NBA of 20 buffers exists. To avoid a wait-for-buffer condition, the DBFX value must be specified as between one or two times the NBA value. This can result in a DBBF specification of three times the NBA number, which gives 60 buffers to the Fast Path buffer pool.

Except for the following case, there is no buffer look-aside capability across transactions or sync intervals (global buffer look-aside).

Assume that a region requests a DEDB CI resource that is currently being written or is owned by another region that ends up being written (output thread processing). Then, this CI and the buffer are passed to the requestor after the write (no read required) completes successfully. Any other regions must read it from disk.