Table 3-2. Without wait time details, the impact calculation can be used to determine the offending latch.

The use of another memory serialization control structure was introduced starting with the Oracle Database 10g Release 2 kernel. Called a mutex, it provides more flexibility and potentially lower performance impact than traditional Oracle latches. Oracle continues to more fully make use of mutexes in each release. Currently, the mutex focus has been in the library cache area. As you'll come to understand, the performance possibilities will entice Oracle kernel developers to increasingly take advantage of the mutex.

The mutex, short for mutual exclusion, is not an Oracle invention. Just like the readv and select system calls, mutexes are available to programmers. A simple Linux manual page request for mutex (man 9 mutex) will return a number of mutex-related calls.