The secondary access method always returns row identifiers so that the database server can locate table rows. The access method can additionally format and return rows from the key columns that the scan descriptor specifies.
Set the am_keyscan purpose flag (with the CREATE SECONDARY ACCESS_METHOD or ALTER ACCESS_METHOD statement) to alert the database server that the am_getnext purpose function returns key values. When am_keyscan is set, the database server knows that am_getnext creates a row in shared memory from the key values in a qualified index entry. If the query selects only the columns in the key, the database server returns rows of index keys to the query. It does not retrieve the physical table row or extract the selected columns from the row.
For more information about am_keyscan, refer to Purpose Options.
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