DMB= parameter for procedures

Use the DMB= parameter in procedure to specify the amount of subpool 231 storage to be allocated to the data management block (DMB) pool.

The value can be specified as either 1- to 6-numeric characters, or 1- to 5-numeric characters followed by either K (kilobyte), M (megabyte), or G (gigabyte). If K, M, or G is not specified, K is the default. The maximum value is 2G-1. If the value specified exceeds 2G-1, the default is 2G-1. The pool size specified is rounded up to the nearest page boundary.

The output of the ACBGEN utility indicates the size of each DMB processed. This output should be examined before specifying the DMB= parameter.

Note:

For IMS, the DMB pool should be large enough to hold all of the non-resident DMBs, as well as any resident DMBs that are changed by the online change function, DDL, or the IMPORT DEFN SOURCE(CATALOG) command.

For Fast Database Recovery (FDBR), the DMB pool must be large enough to hold the largest DMB group that is referenced by any one PSB in the system. During FDBR termination processing, FDBR processes each PSB sequentially. While processing a PSB, FDBR loads all of the DMBs that the PSB has intent for into the DMB pool. After the processing for the PSB is complete, the DMBs it references are cleared from the DMB pool and the next PSB is processed.

If you use the same size DMB pool for both FDBR and IMS, consider the needs of both IMS and FDBR when deciding on the size of the DMB pool. If you define a small DMB pool because most or all of the DMBs are defined to IMS as resident, FDBR may encounter problems trying to backout database changes during FDBR take over.

Note: While an IMS DMB pool is used primarily for non-resident DMBs, if a resident DMB (RES=Y) is changed by the online change function, it will also be loaded into the DMB pool until the next IMS restart. Consequently, if you use both resident DMBs and the online change function, make your IMS DMB pools large enough to accommodate both the non-resident DMBs and any resident DMBs that might be changed in the future by the online change function, DDL, or the IMPORT DEFN SOURCE(CATALOG) command.