V$EVENT_NAME

V$EVENT_NAME displays information about wait events.

Column	Datatype	Description
EVENT#	NUMBER	Number of the wait event
EVENT_ID	NUMBER	Identifier of the wait event
NAME	VARCHAR2(64)	Name of the wait event
PARAMETER1	VARCHAR2(64)	Description of the first parameter for the wait event
PARAMETER2	VARCHAR2(64)	Description of the second parameter for the wait event
PARAMETER3	VARCHAR2(64)	Description of the third parameter for the wait event
WAIT_CLASS_ID	NUMBER	Identifier of the class of the wait event
WAIT_CLASS#	NUMBER	Number of the class of the wait event
WAIT_CLASS	VARCHAR2(64)	Name of the class of the wait event. See "Classes of Wait Events" for a description of the different wait event classes.

The WAIT_CLASS_ID, WAIT_CLASS#, and WAIT_CLASS columns are added to the V$EVENT_NAME view in Oracle Database 10g Release 1 to group wait events by class or category, such as User I/O, Network, Concurrency, etc. The WAIT_CLASS_ID contains the hash value of the wait class name; it will remain the same from version to version as long as the name of the wait class does not change. The column WAIT_CLASS# contains a unique number for the WAIT_CLASS. Just like the EVENT#, it may change from version to version. The column WAIT_CLASS contains the actual name of the wait event class.  

V$SESSION_WAIT

V$SESSION_WAIT displays the resources or events for which active sessions are waiting.

The following are tuning considerations:

• P1RAW, P2RAW, and P3RAW display the same values as the P1, P2, and P3 columns, except that the numbers are displayed in hexadecimal.

• The WAIT_TIME column contains a value of -2 on platforms that do not support a fast timing mechanism. If you are running on one of these platforms and you want this column to reflect true wait times, then you must set the TIMED_STATISTICS initialization parameter totrue. Remember that doing this has a small negative effect on system performance.

  In previous releases, the WAIT_TIME column contained an arbitrarily large value instead of a negative value to indicate the platform did not have a fast timing mechanism.

• The STATE column interprets the value of WAIT_TIME and describes the state of the current or most recent wait.

 

Column	Datatype	Description
SID	NUMBER	Session identifier
SEQ#	NUMBER	Sequence number that uniquely identifies this wait. Incremented for each wait.
EVENT	VARCHAR2(64)	Resource or event for which the session is waiting See Also: Appendix C, "Oracle Wait Events"
P1TEXT	VARCHAR2(64)	Description of the first additional parameter
P1	NUMBER	First additional parameter
P1RAW	RAW(4)	First additional parameter
P2TEXT	VARCHAR2(64)	Description of the second additional parameter
P2	NUMBER	Second additional parameter
P2RAW	RAW(4)	Second additional parameter
P3TEXT	VARCHAR2(64)	Description of the third additional parameter
P3	NUMBER	Third additional parameter
P3RAW	RAW(4)	Third additional parameter
WAIT_CLASS_ID	NUMBER	Identifier of the wait class
WAIT_CLASS#	NUMBER	Number of the wait class
WAIT_CLASS	VARCHAR2(64)	Name of the wait class
WAIT_TIME	NUMBER	A nonzero value is the session's last wait time. A zero value means the session is currently waiting.
SECONDS_IN_WAIT	NUMBER	If WAIT_TIME = 0, then SECONDS_IN_WAIT is the seconds spent in the current wait condition. If WAIT_TIME > 0, then SECONDS_IN_WAIT is the seconds since the start of the last wait, and SECONDS_IN_WAIT - WAIT_TIME / 100 is the active seconds since the last wait ended.
STATE	VARCHAR2(19)	Wait state: 0 - WAITING (the session is currently waiting) -2 - WAITED UNKNOWN TIME (duration of last wait is unknown) -1 - WAITED SHORT TIME (last wait <1/100th of a second) >0 - WAITED KNOWN TIME (WAIT_TIME = duration of last wait)

The text of PARAMETER1, PARAMETER2, and PARAMETER3 of each event are also displayed in the P1TEXT, P2TEXT, and P3TEXT columns in the V$SESSION_WAIT view whenever a session waits on the event. The actual values for these parameters are shown in P1, P2, and P3 columns of the V$SESSION_WAIT view.

V$SYSTEM_EVENT

Column	Datatype	Description
EVENT	VARCHAR2(64)	Name of the wait event
TOTAL_WAITS	NUMBER	Total number of waits for the event
TOTAL_TIMEOUTS	NUMBER	Total number of timeouts for the event
TIME_WAITED	NUMBER	Total amount of time waited for the event (in hundredths of a second)
AVERAGE_WAIT	NUMBER	Average amount of time waited for the event (in hundredths of a second)
TIME_WAITED_MICRO	NUMBER	Total amount of time waited for the event (in microseconds)
EVENT_ID	NUMBER	Identifier of the wait event
WAIT_CLASS_ID	NUMBER	Identifier of the class of the wait event
WAIT_CLASS#	NUMBER	Number of the class of the wait event
WAIT_CLASS	VARCHAR2(64)	Name of the class of the wait event

Note that the TIME_WAITED and AVERAGE_WAIT columns will contain a value of zero on those platforms that do not support a fast timing mechanism. If you are running on one of these platforms and you want this column to reflect true wait times, you must set TIMED_STATISTICS to TRUE in the parameter file;

The column EVENT contains the name of the wait event, and the column TOTAL_WAITS contains the number of times the sessions waited on this event. If applicable to the event, the TOTAL_TIMEOUTS column records the number of times a session failed to get the requested resource after the initial wait. The column TIME_WAITED reports the total amount of time spent waiting on the event. The column AVERAGE_WAIT gives the average time for each wait and is derived from the TOTAL_WAITS and TIME_WAITED olumns. 

Starting with Oracle9i Database, wait time has been tracked in microseconds, that is, 1/1,000,000th of a second, and has been reported in the TIME_WAITED_MICRO column. The TIME_WAITED and AVERAGE_WAIT columns are derived by dividing TIME_WAITED_MICRO by 10000.