Dedicating CPU processors - Oracle affinity Oracle Database Tips by Donald Burleson

Question: I have a 32 CPU Linux server with four large applications and I want to dedicate 4 banks of 8 CPU's of each application.  Is CPU affinity a good practice for Oracle?

Answer: Processor (CPU) dedication is called "CPU affinity", and it's been used for decades on large mainframe computers.

Today, CPU affinity a common technique on large Oracle servers with dozens of applications and Oracle databases to keep any single application from "hogging" all of the processing power.  The downside, of course, is that one application may suffer CPU enqueues (as evidenced by the "r" column of vmstat output).

For complete details on CPU configuration for Oracle, see my book "Oracle Tuning: The Definitive Reference".

Remember, CPU affinity is O/S specific, where you tell the OS to route specific classes of tasks to specific processors:

• Solaris - You can create a processor set:
   
• Linux - You use the Linux processor schedule utility (schedutils)

Oracle also has some hidden parameters that enable/disable CPU affinity, but YOU MUST get the consent of Oracle Technical support before altering an undocumented parms:

_affinity
_enable_default_affinity

 Also see my notes on using the _high_priority_processes parameter to change dispatching priority of background tasks.

If you like Oracle tuning, see the book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts.  You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.