Guidelines for implementation

An access method might create a row from each source record and pass the row to the database server for evaluation. However, each call to mi_row_create() to format a row or to mi_eval_am_qual() to have the database server evaluate the row can reduce performance. A developer might use this simple approach for low-volume data.

If possible, an access method evaluates the entire WHERE clause to eliminate unqualified source records. For each candidate record that it cannot disqualify, the access method calls mi_row_create() and mi_eval_am_qual() functions, which causes the database server to fill in any missing results in the qualification descriptor.