cpu count - cheeyoung/sqlplus-public GitHub Wiki
On CPUs with multiple CPU threads, it specifies the total number of available CPU threads. Various components of Oracle Database are configured based on the number of CPUs, such as the Optimizer, Parallel Query, and Resource Manager.
If CPU_COUNT is set to 0 (its default setting), then Oracle Database continuously monitors the number of CPUs reported by the operating system and uses the current count. If CPU_COUNT is set to a value other than 0, then Oracle Database will use this count rather than the actual number of CPUs, thus disabling dynamic CPU reconfiguration.
When Resource Manager is managing CPU (RESOURCE_MANAGER_PLAN is set), then the database's CPU utilization is limited to CPU_COUNT CPU threads. This feature is called Instance Caging. If Resource Manager is enabled at the CDB level, then the PDB's CPU utilization is limited to the PDB's CPU_COUNT.