RID Pool

The RID pool is used for storing and sorting RIDs for operations such as:

List prefetch
Multiple index access
Hybrid joins
Enforcing unique keys while updating multiple rows

The RID pool is checked by the DB2 optimizer for the prefetch and RID use. The full use of RID POOL is possible for any single user at the run time. Run time can result in a tablespace scan being performed if not enough space is available in the RID. For example, if you want to retrieve 10,000 rows from a 100,000,000 row table and there is no RID pool available, a scan of 100,000,000 rows would occur at any time and without external notification. The DB2 optimizer assumes physical I/O will be less with a large pool.