The Query Optimizer makes use of a Record ID (RID) Pool Buffer when using the list prefetch algorithm for analyzing data access paths. See the section Optimizing Query Processing for more information on the list prefetch algorithm. List prefetch retrieves Record IDs from an index (in response to the constraints of a particular WHERE condition). The RID Pool Buffer is used to store the Record IDs. If required, the records are sorted before being stored in the RID Pool Buffer.
If the number of Record IDs fetched exceeds the available RID Pool size, the list prefetch is aborted and less efficient processing routines are used. For best performance, the size of the RID Pool Buffer should be large enough to contain the number of Record IDs expected from an index search.
The RID Pool size is specified in the XDBRIDPOOL environment variable in the server machine's configuration file. See XDBRIDPOOL in the appendix Environment Variables for more information on using this environment variable, and for a formula for calculating RID Pool Size.