Virtual storage considerations for SB

Each DB-PCB/DSG pair buffered by SB has its own SB buffer pool.

By default, each SB buffer pool contains four buffer sets (although IMS lets you change this value). Ten buffers exist in each buffer set. Each buffer is large enough to hold one OSAM data set block.

 4 * 10 * block size

The SB buffers are page-fixed in storage to eliminate page faults, reduce the path length of I/O operations, and increase performance. SB buffers are page-unfixed and page-released when a periodic evaluation temporarily deactivates SB.

You must ensure that the batch, online or DBCTL region has enough virtual storage to accommodate the SB buffer pools. This storage requirement can be considerable, depending upon the block size and the number of programs using SB.

SB is not recommended in real storage-constrained environments such as batch and DB/TM.

Some systems are storage-constrained only during certain periods of time, such as during online peak times. You can use an SB Initialization Exit Routine to control the use of SB according to specific criteria (the time) of day.