Figure 2-8 is a 30-second interval snapshot based on v$system_event. The report swpctx.sql is part of OraPub's System Monitor (OSM) tool kit, which is a free and easy-to-use performance diagnostic tool kit available from OraPub's web site. Notice there are no session-level references. Session-level information is available in v$session_event and v$session_wait. The top wait event is clearly db file scattered read. In fact, sessions are spending 53% of their Oracle wait time on this single wait event.

Figure 2-8. A classic instance-level interval (30 s) wait event report based on v$system_event. The top wait event is db file scattered read, followed by read by other session.

It is common to misunderstand what Oracle's wait interface is telling us. The information in Figure 2-8 is not referring to Oracle response time, end user response time, or what the users are experiencing. The top wait event's 53% value refers only to the wait time component of the Oracle response time; that is, what Oracle's kernel code instrumentation has provided.