within a regional instance, the configuration is made up of a primary instance and a standby instance.
Shared-core machines are good for prototyping, and are not covered by Cloud SLA
Each vCPU is subject to a 250 MB/s network throughput cap for peak performance.
More core increases the network cap, up to a theoretical maximum of 2000 MB/s.
For performance-sensitive workloads such as online transaction processing (OLTP), a general guideline is to ensure that your instance has enough memory to contain the entire working set and accommodate the number of active connections.