不能忽略 .htaccess 对性能的影响
在Apache环境下使用 .htaccess 进行URL重写或许已经是一种非常常用的方式；然而，如果URL重写规则比较复杂，使用.htaccess的方式可能会影响到Apache的性能。
测试方式
一个简单的echo语句，分别进行以下测试：
- allowoverride=none,无rewrite
- allowoverride=all,无.htaccess
- allowoverride=all,简单的.htaccess
- allowoverride=none,简单的rewrite
- allowoverride=all,复杂的.htaccess
- allowoverride=none,复杂的rewrite
结果
先说结果，当rewrite规则比较简单时，性能影响不大，17201 vs 19486。
当rewrite规则比较复杂，超过900行，有较多正则表达式，跳转（用来做栏目rewrite），性能变化较大 1497 vs 7108
如果访问的目录路径比较深，在allowoverride开启的情况下，apache需要历遍每一个目录去读取.htaccess，性能的影响理论上会更大，测试数据 15623 vs 17201（7层目录vs根目录）。
当然，在实际应用场景中，相对PHP跟Mysql而言，Apache的这点性能损失可能不算什么；但是，只需要简单的将rewrite规则从htaccess复制到apache.conf中就可以得到性能的提升，何乐而不为呢？ :)
测试数据
allowoverride=none，无rewrite
Concurrency Level: 10
Time taken for tests: 0.500 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 20008.88 [#/sec] (mean)
Time per request: 0.500 [ms] (mean)
Time per request: 0.050 [ms] (mean, across all concurrent requests)
Transfer rate: 3673.51 [Kbytes/sec] received
allowoverride=all，无.htaccess
Concurrency Level: 10
Time taken for tests: 0.491 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 20371.66 [#/sec] (mean)
Time per request: 0.491 [ms] (mean)
Time per request: 0.049 [ms] (mean, across all concurrent requests)
Transfer rate: 3740.11 [Kbytes/sec] received
简单的.htaccess(符合单入口文件类的网站)
Concurrency Level: 10
Time taken for tests: 0.581 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 17201.99 [#/sec] (mean)
Time per request: 0.581 [ms] (mean)
Time per request: 0.058 [ms] (mean, across all concurrent requests)
Transfer rate: 3158.18 [Kbytes/sec] received
简单.htaccess，访问 /a/b/c/d/e/f/g/ 路径
Concurrency Level: 10
Time taken for tests: 0.640 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 15623.29 [#/sec] (mean)
Time per request: 0.640 [ms] (mean)
Time per request: 0.064 [ms] (mean, across all concurrent requests)
Transfer rate: 2868.34 [Kbytes/sec] received
简单的rewrite规则，写入apache.conf
Concurrency Level: 10
Time taken for tests: 0.513 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 19486.15 [#/sec] (mean)
Time per request: 0.513 [ms] (mean)
Time per request: 0.051 [ms] (mean, across all concurrent requests)
Transfer rate: 3577.54 [Kbytes/sec] received
复杂的.htaccess(900行，使用正则表达式对栏目内容进行映射，还有对旧内容的重定向等)
Concurrency Level: 10
Time taken for tests: 6.677 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 1497.75 [#/sec] (mean)
Time per request: 6.677 [ms] (mean)
Time per request: 0.668 [ms] (mean, across all concurrent requests)
Transfer rate: 274.98 [Kbytes/sec] received
将规则写入apache.conf，并且禁用allowoverride后：
Concurrency Level: 10
Time taken for tests: 1.407 seconds
Complete requests: 10000
Failed requests: 0
Total transferred: 1880000 bytes
HTML transferred: 10000 bytes
Requests per second: 7108.94 [#/sec] (mean)
Time per request: 1.407 [ms] (mean)
Time per request: 0.141 [ms] (mean, across all concurrent requests)
Transfer rate: 1305.16 [Kbytes/sec] received