《Systems Performance: Enterprise and the Cloud》读书笔记系列（二） —— 第二章（一）

分析Systems Performance常用术语简介：

1. IOPS: Input/Output operations per second is a measure of the rate of data transfer operations. For disk I/O, IOPS refers reads and writes per second.

2. Throughput: the rate of work performed. Especially in communications, the term is used to refer to data rate ( bytes per second or bits per second). In some contexts(e.g., databases), throughput can refer to the operation rate ( operations per second or transactions per second).

3. Response time: the time for an operation to complete. This includes any time spent waiting and time spent being serviced (service time), including the time to transfer the result.

4. Latency: Latency is a measure of time an operation spends on waiting be serviced. In some contexts, it can refer to the entire time for operation, equivalent to response time.

5. Utilization: For resources that service requests, utilization is a measure of how busy a resource is, based on how much time in a given internal it was actively performing work. For resources that provide storage, it may refer to the  capacity that is consumed(e.g., memory utilization).

6. Saturation: the degree to which a resource has queued work which it cannot service.

7. Bottleneck: In system performance, a bottleneck is a resource that limits the performance of the system. Identifying and removing the bottlenecks is a key activity of systems performance.

8. Workload: The input to the system or the load applied is the workload. For a database, the workload consists of the database queries and commands sent by the clients.

9. Cache: a fast area that can duplicate or buffer amount of data, to avoid communicating directly with a slower tier of storage, thereby improving performance. For economical reasons, a cache is smaller than the slower tier.