Oracle Tips by Burleson

Oracle10g Grid Computing with RAC
Chapter 7 - Cache Fusion and Inter Instance Coordination

Oracle uses several processes to execute the different parts of Oracle code and to spawn additional processes for the users. Whenever a user connects to the database, a new server process is created on behalf of the user session.

• Parse and execute SQL statements issued through the application. §   Read the necessary data blocks from the disk data files into the shared database buffers of the SGA, if the blocks are not already present in the SGA.
   
• Interact and return results in such a way that the application can process the information.

Locking Mechanism

Locking is another important requirement of a multi-version consistency model. Oracle also uses a locking mechanism to control concurrent access to the data blocks. Locks help prevent destructive interaction between users accessing data blocks. As seen earlier, when a user intends to update a data block that has already been updated by another user, but is still in an uncommitted state, the update event has to wait. Without a lock mechanism, the data integrity would have been lost in this case. Locks also ensure that the data being viewed or updated by a user is not changed (by other users) until the user is finished using the data.