OCA Oracle Database 11g: Database Administration I: A Real-World Certification Guide

Managing serialization mechanisms

The concurrency mechanisms that we explored thus far involve mainly maintaining multiple versions of a block and displaying the correct version of a given block to a user. There are, however, other mechanisms that serialize access to table rows, database objects, or other system resources. As an RDBMS cannot allow two users to operate on the same piece of data at exactly the same time, it must have rules in place that prevent such an occurrence. As a simple example, imagine a four-way traffic stop. As more than one automobile cannot cross the same space at the intersection at exactly the same time, control mechanisms such as a traffic light must be employed to prevent collisions. In a similar manner, Oracle uses ...