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Oracle数据库latch和mutex等待事件全面解析
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2024-05-13
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Oracle数据库latch和mutex等待事件全面解析
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Latch and Mutex Contention
Troubleshooting in Oracle
Tanel Põder
http://blog.tanelpoder.com
Tanel Põder http://www.tanelpoder.com 2
If you like this session...
...then you're probably an Oracle geek like me ;)
And you will like my tech-blog:
http://blog.tanelpoder.com
All my scripts freely downloadable
http://blog.tanelpoder.com/seminar/seminar-files/
Look for TPT scripts
Oh... and I do seminars with much more stuff like this ;-)
And I also fix these kinds of problems as a consultant
http://blog.tanelpoder.com/seminar/
tanel@tanelpoder.com
Tanel Põder http://www.tanelpoder.com 3
Intro to latching - 1
What is a latch?
Oracle's low-level mechanism for serializing concurrent access to
very shortly accessed memory structures such as cache buffer
headers etc...
Yeah, but what is a latch?
Latch is just a simple memory structure
Usually around 100-200B in size (dependent on version,platform)
Is wrapped into a latch state object structure (since v8.0 I think)
Can reside in fixed SGA (parent latches) or shared pool
Is set using hardware-atomic compare-and-swap (CAS) instructions
•
LOCK CMPXCHG on intel
Latches are taken and released without any OS interaction
•
Actually the OS doesn't even have a clue that Oracle latches exist!
Can be shared (since Oracle 8.0)
•
Used for some AQ ops
•
For example, used for cache buffers chains latch gets if examining a
buffer chain
Blah blah
blah!
Tanel Põder http://www.tanelpoder.com 4
The real intro to latching
Latch is a lock
period.
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