High CPU usage of database

In my experience ,Oracle database is capable of taking good amount of load and can utilize the hardware power very effectively for scaling. However in some case , you might find that the CPU usage by the database is considerably high. In my experience , these factors can also cause a high CPU utilization

• Queries performing excessive work to achieve desired results. This could be more data blocks scanning, more nested loops etc.
• Table setups can be cause of concern if there is large amount of row chaining etc.
• Large amount of house keeping work on database like archival sweep, rman processes etc.
• Application keeps opening new physical connections to the database instead of using the connection pool. Even though application servers configure the connection pool, the connection pool might open new physical connections for all transactions due to wrong set up of connection pool.
• XA Transaction has a higher impact on the database as it needs to perform the house keeping activity like managing the transactions stages like prepare, commit etc .
• When less number of CPUs are present and more number of processes are present on the system, the system usage will go high due to context switching.
• As a matter of fact, the CPU utilization will go invalid or the system starts behaving in an awkward manner when the CPU utilization hits above 85%.

In some cases, correcting the above symptoms would fix the high CPU usage. However , in many other cases, it might be that the applications needs that much processing power to support the database operations.