Parallelism and resource usage

Learning parallelism in our newly inherited DW. We have 32 cores in the server. I kicked off a simple count(*) on a multi billion row table (no one working at that time) and i saw the Oracle use a parallelism of 64 for the query. I checked the degree of parallelism for the table which was set at DEFAULT. It looks like oracle multiplied the cpu_count and parallel_threads_per_cpu (2) and assumed a degree of parallelism of 64.

I monitored the OS CPU usage, it was anywhere from 20% to 30% used overall, with individual core usages varying from 0% to 100%.

This makes me wonder how oracle will behave when there are simultaneous multiple big parallel queries. If two or three such queries are started I wonder how it will behave (I did not test that) before the server chokes on CPU. I remember reading about features like PAMU (parallel_adaptive_multiuser) and similar such parameters used to control the parallelism of running jobs. I would like to learn more about such parameters both for 12c and 19c; We may move from current 12c to 19c. Any pointers?

I am also happy with the responses here, since they give a good overall picture or guide me in the right direction. I am aware that things have been evolving in that area over different versions.

CP

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