DBMS_MONITOR is a wonderful Oracle package. While it does not solve all profiling challenges, it is truly a giant leap forward. It's flexibility in purpose and use, and the fact that no additional license is required make it something every Oracle DBA should at least be familiar with.

Some would say instrumentation is the best performance statistics gathering approach, but others would say periodic sampling is the best. After all, nearly all third-party tools rely on polling, which is sampling. Just as Iron Man's Tony Stark would say, "Is it too much to ask for both?" And this is exactly what Oracle has done.

The classic performance view v$sysstat is based on instrumentation, since when a database call completes, the respective statistics are updated. The wait interface is clearly an instrumentation approach, with the additional gettimeofday system calls inserted into Oracle's kernel code. The time model views are based on a combination of instrumentation (since the view is not updated if a session is in the middle of a wait) and sampling due to the frequent getrusage calls. But with the introduction of Oracle's active session history, or ASH for short, Oracle has clearly implemented a very aggressive statistical sampling collection strategy. So Oracle has indeed begun using both instrumentation and sampling.