为什么要做性能测试？
1、The failure of a mission-critical application can be costly
2、Assure performance and functionality under real-world conditions.
3、Locate potential problems before your customers do.
4、Reduce development time and infrastructure costs.
性能测试的类型：
Component testing（组件测试）：find the behavior. and performance of eachtier.
Load testing：find out whether the system can handle the expected load upon deployment eunder realworld conditions
Stress testing：find the system’s breaking point .apply testing that measures whether the systems environment is properly configured to handle expected or potentially unexpected high rransaction volumes
容量测试：find the stability of the system with respect handling large amounts of data over extended time periods
性能测试的一些例子：
Application response time
Configuration sizing
Acceptance稳定性
Regression回归测试
Reliability
Capacity planning容量规划
Bottleneck identification瓶颈确定
Product evaluation
性能测试贯穿于软件生命周期：
Planning and design——development——deployment——production——evolution
解决方案：
Overcomes resource limitations
Replaces testers with “virtual users”
Runs many vusers on few machines
Controller manages virtual users
Allows repeatable tests with scripted actions
Provides meaningful results with analysis tools
LR对系统性能的监控：
Monitors are non-intrusive and agent-less
Monitors Gather data for online/offline analysis
Monitors Display real-time data during testing
Monitors Gather data for offline root cause analysis after testing
