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Inside the Real-time v$ Wait Events

The foundation concept of the ASH architecture is called the time model, and Oracle10g has introduced several important wait event v$ views.  Table 16.4 below shows some v$ equivalents to dba_hist views.

 

v$ View

dba_hist View

v$active_sess_hist

dba_hist_active_sess_history

v$sys_time_model

dba_hist_sys_time_model

v$active_session_history

dba_hist_active_sess_history

v$event_histogram

No equivalent DBA view

Table 16.4: Oracle v$ equivalents to ASH wait event tables

 

The main components of OWE interface are the dynamic performance views: v$session _wait  ; and v$session_event as shown in Figure 16.8.

 

Figure 16.8: The v$ event structures in Oracle10g

 

These v$ views are in-memory structures that feed data to the ASH tables which provide time-series wait event information. 

The ASH samples for wait events every second and tracks the waits in the new v$active_sess_hist view.  Before looking into the wrh$ and ASH tables, it will be useful to take a quick tour of the important v$ wait event views.

SEE CODE DEPOT FOR FULL SCRIPTS


This is an excerpt from my latest book "Oracle Tuning: The Definitive Reference". 

You can buy it direct from the publisher for 50%-off and get instant access to the code depot of Oracle tuning scripts:

http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm

 

 

   

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