Exadata Wait Events

The Oracle database is a very well-instrumented piece of code, and it has been so for quite a while. It keeps track of the amount of time spent in discrete operations via the use of wait events, unless the session in question is on the CPU. While the database software is quite complex, wait event analysis allows performance analysts to determine where the database is spending its time. Many difficult performance problems can be resolved by analyzing data from the wait interface and, more recently, the Active Session History (ASH). The introduction of Exadata has resulted in the creation of several new wait events to support the unique operations that are performed on the platform. This chapter will focus on describing these new events and how they relate to the activities actually being performed, while contrasting them with the wait events used by the database on non-Exadata platforms. It will also describe a few wait events that are not specific to Exadata but play an important role on Exadata platforms.