Oracle Internals: An Introduction

Advanced Latching Control

Some operating systems support a facility called multi-processing control. This enables an authorized user process to influence its CPU scheduling in a variety of ways. Where available, Oracle can use certain multi-processing control features. The following features affect the latching mechanism.

Preemption Control

Preemption control enables Oracle to suspend the operation of the normal operating system process preemption mechanism during performance-critical operations—in particular, when holding a latch. This means that the Oracle process can continue to run on its CPU until it explicitly enables preemption again, or until it blocks on an operating system event such as an I/O request, semaphore operation, or page fault. The process will not be pre-empted at the end of its time-slice by a higher priority process of the time-sharing priority class. This means that operations protected by latches complete as quickly as possible, and so the risk of latch contention is greatly reduced. If preemption control is available to Oracle, it is used by default unless disabled using the _NO_PREEMPT parameter.

CPU Yielding

CPU yielding enables Oracle processes to offer to yield the CPU during a spin. If there is another runnable process of higher priority able to use the CPU, that process is scheduled, and the yielding process is placed at the end of its run queue, but it remains runnable. Otherwise, if there are no other higher-priority processes able to use the CPU, ...