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Connor McDonald

Thanks for the question, oracle.

Asked: January 09, 2017 - 9:05 am UTC

Last updated: January 11, 2017 - 6:05 am UTC

Version: 11.2.0

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You Asked

Hi,

I have awr report in there Foreground events are there can you pls help to know how to solve this events to improve the db performance.

Top 5 Timed Foreground Events

library cache: mutex X
DB CPU
log file switch (checkpoint incomplete)
db file parallel read
resmgr:cpu quantum


Thanks

and we said...

Just because something is at the top of the list does not necessarily mean that it is "bad". You need to consider the time that each contributes compared to overall time and resource consumption on your database.

For example, if 60 seconds of "library cache: mutex X" at the top, and that is from a 61 second sample, than you have a big issue. If on the other hand it is from a 4 hour sample, then it is insignificant.

Anyway, here is a brief explanation for each of these wait events:

library cache: mutex X
=> related to concurrency. Processes compete for shared resources in the library cache, and to control who has access at any given point in time, we use mutexes, which are like lightweight latches, ie, structures to ensure that two people (processes) are not changing the same memory structure at the same time.

log file switch (checkpoint incomplete)
=> we wanted to reuse a redo log file but the underlying checkpoint to ensure all the database changes backed by that redo log was flushed to disk.

resmgr:cpu quantum
=> resource manager throttled back some process or processes because they were consuming excessive CPU.

We can't really deduce much without the full report, but typically, when we start seeing 'library cache: mutex X' and 'resmgr:cpu quantum' together, it often means the box is under CPU pressure, often from excessive parsing.

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Comments

oracle oracle, January 10, 2017 - 11:08 am UTC

Thanks for Reply,

Can you pls let me know what is the solution or what things that needs to check when these wait events came.

Thanks
Connor McDonald
January 11, 2017 - 6:05 am UTC

The occurrence of a wait event is not important.

The *impact* of a wait event (or CPU) is what matters.


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