ab的原理：ab命令会创建多个并发访问线程，模拟多个访问者同时对摸一个URL地址进行访问。它的测试目标是基于URL的，因此它既可以用来测试apache的负载压力，也可以测试nginx、lighthttp、tomcat、IIS等其他web服务器的压力。

$ ab -n1000 -c10 http://localhost:3000/

1000条请求，10个并发

相关参数：

-n requests     Number of requests to perform-c concurrency  Number of multiple requests to make at a time-t timelimit    Seconds to max. to spend on benchmarking                This implies -n 50000-s timeout      Seconds to max. wait for each response                Default is 30 seconds-b windowsize   Size of TCP send/receive buffer, in bytes-B address      Address to bind to when making outgoing connections-p postfile     File containing data to POST. Remember also to set -T-u putfile      File containing data to PUT. Remember also to set -T-T content-type Content-type header to use for POST/PUT data, eg.                'application/x-www-form-urlencoded'                Default is 'text/plain'-v verbosity    How much troubleshooting info to print-w              Print out results in HTML tables-i              Use HEAD instead of GET-x attributes   String to insert as table attributes-y attributes   String to insert as tr attributes-z attributes   String to insert as td or th attributes-C attribute    Add cookie, eg. 'Apache=1234'. (repeatable)-H attribute    Add Arbitrary header line, eg. 'Accept-Encoding: gzip'                Inserted after all normal header lines. (repeatable)-A attribute    Add Basic WWW Authentication, the attributes                are a colon separated username and password.-P attribute    Add Basic Proxy Authentication, the attributes                are a colon separated username and password.-X proxy:port   Proxyserver and port number to use-V              Print version number and exit-k              Use HTTP KeepAlive feature-d              Do not show percentiles served table.-S              Do not show confidence estimators and warnings.-q              Do not show progress when doing more than 150 requests-l              Accept variable document length (use this for dynamic pages)-g filename     Output collected data to gnuplot format file.-e filename     Output CSV file with percentages served-r              Don't exit on socket receive errors.-m method       Method name-h              Display usage information (this message)-Z ciphersuite  Specify SSL/TLS cipher suite (See openssl ciphers)-f protocol     Specify SSL/TLS protocol