Improved EDM pool management

Db2 12 introduces improved performance for Db2 database systems that have large EDM pools and run multiple, concurrent threads.

These improvements can lead to somewhat higher real storage usage by the database system.

As part of these changes, how EDM pool storage is allocated for certain types of structures has changed.

Previously, the following subsystem parameters determined the amount of storage that was initially allocated in the EDM pool for each type of structure:

• EDMDBDC for the DBD cache
• EDMSTMTC for the dynamic statement cache
• EDM_SKELETON_POOL for the EDM skeleton pool

After the initial allocation, the values could be increased or decreased, but the values could never be less the values that were specified at installation time.

In Db2 12, no storage is initially allocated for these structures. Storage is allocated as it is needed. When the values are reached, and more storage is needed, structures that are not currently in use are removed to keep the storage that is in use below the specified values.