Background

The Wait Interface started to appear in the Oracle RDBMS in version 7. However, the Wait Interface first started to become more widely known with Anjo Kolk’s YAPP (Yet Another Performance Profiling) Method paper published in 1999. Since that time, many more people have written about it in technical white papers and articles and spoken about it at user groups and conferences.

So, What is the Wait Interface?

Wait Interface is the name that has been given to the mechanism in an Oracle database that allows the Remote DBA to look into the internal workings. This allows the Remote DBA to see what various components are doing by looking at where they are spending their time waiting. While some wait-related information can be gathered by other views, the three main views that examine the Wait Interface are:

* v$system_event

* v$session_event

* v$session_wait

Why are these three views the key? A review of what information they each contain and a sample of their output may help illustrate their importance. Remember to enable timed statistics in the database by using the timed_statistics=TRUE parameter in the init.ora file or spfile or by altering the system using:

ALTER SYSTEM SET TIMED_STATISTICS = TRUE;

Otherwise, there will be no timing information. Oracle says there is a small impact on the system when this is turned on, but most agree that anyone on any recent Oracle version should generally leave this on all the time. In theory, there may be a performance penalty for a mechanical speedometer in a car, but that doesn’t mean people looking for optimum performance remove their speedometer. The information provided by the speedometer more than offsets its small performance impact. Likewise, the performance impact of enabling timed_statistics compared to the availability of better information on how the database is performing.

The above book excerpt is from:

Oracle Wait Event Tuning

High Performance with Wait Event Interface Analysis

ISBN 0-9745993-7-9

Stephen Andert

http://www.rampant-books.com/book_2004_2_wait_tuning.htm