At DOAG Exaday 2018 Martin Bach talked about using the Resource Manager. He explained, that Resource Manager is using the CPU_COUNT initialization parameter to limit the CPU utilization of a database instance. This is called instance caging and requires an Enterprise Edition License. Resource Manager is not available in Standard Edtion 2 (SE2) according to the Licensing Guide:
On the other hand, SE2 is limited to 16 threads per database. Franck Pachot did investigate this in his blog post and found out, that internally Resource Manager features are being used to enforce this limitation.
So the question came up, what will happen to a SE2 Oracle Database that has CPU_COUNT set. According to the documentation, CPU_COUNT works only with Resource Manager which is not part of SE2, but SE2 is using Resource Manager internally.
Now, let’s try. I did use the same method to generate load that Franck Pachot used for his tests. A simple PL/SQL block running in several database jobs. For testing this, I set CPU_COUNT to 4 and did run 10 parallel jobs. Having this, my workload is definitely below the internal maximum of 16 threads. To measure the workload I used top, oratop and Statspack, database version was 22.214.171.124.171017.
And these are the results. My server (ODA X7-2S, 1 CPU, 10 cores hyperthreaded) had an utilization of roughly 20% plus a little overhead. Having 20 cores in the OS and a CPU_COUNT of 4, I end up with a maximum of 1/5th of the server that I can utilize. In other words: 20%. This is what “top” showed:
To see, what the database instance is actually doing, I used “oratop”:
You see, there are 4 session on CPU and some others waiting for Resource Manager. That proofes, that SE2 internal Resource Manager is using the CPU_COUNT parameter to limit the utilization. Finally, let’s check the Statspack report:
In this overview you can see the 10 sessions that are trying to do something (DB time) and the 4 sessions that are actually doing some work on CPU (DB CPU).
Conclusion / Disclaimer
Instance caging does work in a SE2 Oracle Database. You can limit the database to use even less than 16 threads. But the fact that this works does not necessarily mean that it is allowed. So use in case you use this featuer, you do that on your own risk.
Edit: Dominic Giles stated in the Twitter discussion that it is allowed to do instance caging in SE2.