BUG - High "row Cache Mutex" Waits - Oracle 19c

Today, during an analysis of a performance problem in Oracle 19c, I found an event strange that I had not seen before.
I started looking at the event “ROW CACHE MUTEX” with a large number of events in 1 hour of process execution.



We can see above in 1 hour of processing we had 2,184,882 events with consumption of 51.92% of DB time. 
 I can found this bug in Oracle Support
Bug 31933451 – High “row Cache Mutex” Waits (Doc ID 31933451.8)
  • Hang (Involving Shared Resource)
  • Internal Error May Occur (ORA-600)
  • Waits for “Row Cache Mutex”
Too many row cache objects are being copied or ‘cloned’.  This fix ensures that only the ‘hot’ objects are cloned, not every object on the hash chain.
This problem affects all versions 19.x. 
There is no workaround for this problem.
In version 21.1 is fixed the problem.
There is already a specific one-off patch for this released in December.
After the patch was applied, an AWR collection was performed again and we could see that it resolved with an impressive result.
We had a 95.72% reduction in the “ROW CACHE MUTEX” event contention.
I hope I helped with this article
Stay tuned, following on twitter @aontalba and on Linkedin
Andre Ontalba


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