Access to Data in Fragmented Tables with Rowid

From the viewpoint of an application, the functionality of a rowid column in a fragmented table is identical to the rowid of a nonfragmented table. However, unlike the rowid of a nonfragmented table, the database server uses an index to map the rowid to a physical location.

When the database server accesses a row in a fragmented table using the rowid column, it uses this index to look up the physical address of the row before it attempts to access the row. For a nonfragmented table, the database server uses direct physical access without an index lookup. As a consequence, accessing a row in a fragmented table using rowid takes slightly longer than accessing a row using rowid in a nonfragmented table. You should also expect a small performance impact on the processing of inserts and deletes due to the cost of maintaining the rowid index for fragmented tables.

Primary-key access can lead to significantly improved performance in many situations, particularly when access is in parallel.