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Cache affinity of processor affinity is the binding of a process to a specific CPU. Historically, the presumption has been that since a certain CPU is running a process, there is a good chance that the process will benefit if it is run on the same CPU next time. Specially, it is assumed that the process might be able to reuse the data in the CPU level-1 cache, thus avoiding having to read physical memory. For most modern Oracle applications, however, this is rarely true. That’s because the CPU L1 Cache is too small to store anything of real value. Also, any performance benefit (may be a few nanoseconds) derived would be negligible. Newer uniprocessor and SMP machines are implementing shorter buses linking the CPU to physical memory. Hence, access to physical memory is blazingly fast nowadays. However, technical experts and gurus at some sites insist on using processor affinity to enhance performance. What they end up getting in return is increased administrative overhead and performance degradation. Since processor binding forces a certain process to use only certain CPU, the process will have to wait or sleep if that CPU happens to be busy running another process. Even if other CPUs are available at the time, the process cannot be run by them. Such scenarios are extremely common at sites running both OLTP and DSS applications. In trying to decrease system load level, do not resort to methods that may instead impede performance and bar optimal usage of resources. At various times, we all encounter users who tend to run huge queries during peak production hours and they often are the first to complain about performance. This is more prevalent in companies having DSS systems such as data warehouses and data marts. Somehow, the job that was meant to run late at night to populate the warehouse ends up running during peak morning or early afternoon hours. Make sure that you detect and prevent such non production or non mission critical tasks from taking up valuable resource like memory and CPU. About Author: Gitesh Trivedi has 14+ years of experience and providing Remote Oracle Support and also author of online Oracle Trainings courses.
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processor affinity, oracle server, database server, tuning, performance tuning,
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