Study Notes

Throttling is one of the three effective methods for protecting a high concurrency system. The other two are respectively caching and downgrading. Throttling is used in many scenarios to limit the concurrency and the number of requests. Our service has tens of millions of TPS, with tens of thousands of hosts serving traffic. Throttling is vital for such a large distributed service.

DynamoDB was announced by Amazon CTO Werner Vogels on in 2012, 14 years after NoSQL was proposed in 1998. It supports key-value and document-oriented structure storage.

In Computer Systems, the CPU is much faster than the storage system, so ideally we want storage system read/write as fast as possible, unfortunately, the price of storage media increases exponentially with the access speed. Thus, in order to balance cost and performance, we designed a multi-layer memory hierarchy.

CPU Scheduling is a process of determining which process will own CPU for execution while another process is on hold. The main task of CPU scheduling is to make sure that whenever the CPU remains idle, the OS at least selects one of the processes available in the ready queue for execution.

In order to improve CPU utilization, and more effectively manage jobs in a multiprogramming system, the operation system(OS) abstracts the “process”. Each process has a Process Control Block(PCB*) which contains all information that OS required to manage the process, and resources in user space memory, they’re generally independent of each other, but the kernel space is shared, so communication between processes must go through the kernel.