Apache Architecture：

How do we measure performance? 如何测量web服务器的性能？

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–Requests per Second 每秒请求次数

–Bandwidth 带宽

–Latency 等待时间

–Concurrency (Scalability) 并发（可扩展）

Building a scalable web server：设计可扩展的web server

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handling an HTTP request 处理http请求

–map the URL to a resource 将url映射成资源

–check whether client has permission to access the resource 检查客户端是否有访问资源的权限 –choose a handler and generate a response 选择处理器和生成响应

–transmit the response to the client 发送响应到客户端

–log the request 记录请求日志

must handle many clients simultaneously 必须同时处理多个请求

must do this as fast as possible 必须尽可能快的处理

Resource Pools：资源池

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one bottleneck to server performance is the operating system 服务器性能瓶颈之一是操作系统

–system calls to allocate memory, access a file, or create a child process take significant amounts of time

分配内存，访问文件和创建子进程的系统调用会消耗大量时间

–as with many scaling problems in computer systems, caching is one solution

计算机系统中的许多扩展性的问题，缓存是一种解决方法

resource pool: application-level data structure to allocate and cache resources 应用层数据存储的分配和缓存资源

–allocate and free memory in the application instead of using a system call?

在应用中分配和释放内存，用来代替使用系统调用

–cache files, URL mappings, recent responses?

缓存文件，url映射，最近产生的回复（响应）

–limits critical functions to a small, well-tested part of code?

把至关重要的函数限制到小的，充分测试的代码

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Multi-Processor Architectures：多处理器体系结构

a critical factor in web server performance is how each new connection is handled

web服务器性能至关重要的因素之一就是每一个连接如何被处理

–common optimization strategy: identify the most commonly-executed code and make this run as fast as possible

通常的优化策略：识别最频繁执行的代码并且让它执行的尽可能快

–common case: accept a client and return several static objects

通常的情况：接受客户端请求，返回几个静态对象

–make this run fast: pre-allocate a process or thread, cache commonly-used files and the HTTP message for the response

让这运行的更快：预分配线程或进程，缓存经常使用的文件和http消息

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Connections：连接

must multiplex handling many connections simultaneously 必须同时处理多个连接