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How to understand v$system_event, I believe that many inexperienced people are at a loss about it. Therefore, this paper summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

V$session_wait shows the current wait items of the system, while v$system_event provides a summary of each wait event since the instance was started. It is often used to obtain historical images of system waiting information. By getting the increment of wait items through two snapshot, you can determine the wait items of the system during this period of time.

Common columns in v$system_event

EVENT: wait event name

TOTAL_WAITS: the total number of waits for this event

TIME_WAITED: the total wait time for this event (in 1% seconds)

AVERAGE_WAIT: the average wait time for this event (in 1% seconds) (time_waited/total_waits)

TOTAL_TIMEOUTS: the total number of times this item has timed out

Note:

If there is waiting for (something), there may be waiting for the event that does not come, that is, the so-called waiting timeout.

Example:

1. View the waits of the system, sorted by total time spent

SELECT event,total_waits waits,total_timeouts timeouts

Time_waited total_time,average_wait avg

FROM V$SYSTEM_EVENT

ORDER BY 4 DESC

For example, you can view the performance of checkpoint processes through checkpoint completed, log file switch (checkpointincomplete). You can view the performance of online redo log files through log file parallel write and log file switchcompleted. The performance of the archiving process can be checked through the log file switch (archivingneeded) event.

Select sum (total_waits) waits,sum (total_timeouts) timeouts from v$system_event where event like''enq%''

Identify bottlenecks:

one. List idle events through Statspack.

two. Check the wait time overhead for different events.

three. Check the average time spent waiting for each record, because some wait events (compare log file switchcompletion) may occur periodically, but cause significant performance loss when they occur.

After reading the above, have you mastered how to understand v$system_event? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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