Using Apache Bench for Simple Load Testing

If you have access to a Mac or Linux server, chances are you may already have a really simple http load generating tool installed called Apache Bench, or ab. If you are on windows and have Apache installed, you may also have ab.exe in your apache/bin folder.

Suppose we want to see how fast Yahoo can handle 100 requests, with a maximum of 10 requests running concurrently:

ab -n 100 -c 10 http://www.yahoo.com/

It will then generate output as follows:

Concurrency Level:      10
Time taken for tests:   1.889 seconds
Complete requests:      100
Failed requests:        0
Write errors:           0
Total transferred:      1003100 bytes
HTML transferred:       949000 bytes
Requests per second:    52.94 [#/sec] (mean)
Time per request:       188.883 [ms] (mean)
Time per request:       18.888 [ms] (mean, across all concurrent requests)
Transfer rate:          518.62 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       57   59   1.7     59      64
Processing:   117  126   7.5    124     162
Waiting:       57   62   7.0     60      98
Total:        175  186   8.0    184     224

Percentage of the requests served within a certain time (ms)
  50%    184
  66%    186
  75%    187
  80%    188
  90%    192
  95%    203
  98%    216
  99%    224
 100%    224 (longest request)

As you can see this is very useful information, it returned requests at a rate of 52.94 requests per second, the fastest request was 175ms, the slowest 224ms

So the next time you are tempted to whip out cfloop and GetTickCount to do some benchmarking on a piece of code, give ab a try, it's easy to use, and will yield much more realistic results.

Because ab supports concurrency, this has two big advantages over cfloop. The main one is that it allows you to test how your code runs concurrently, this can help you identify any possible race conditions, or locking issues. Concurrent requests are also a more natural simulation of load than loops.

Suppose you wanted to test multiple url's concurrently as well? You can do this by creating a shell script, with multiple ab calls. At the end of each line place an & this makes the command run in the background, and lets the next command start execution. You will also want to redirect the output to a file for each url using > filename For example:

#!/bin/sh

ab -n 100 -c 10 http://127.0.0.1:8300/test.cfm > test1.txt &
ab -n 100 -c 10 http://127.0.0.1:8300/scribble.cfm > test2.txt &

The usage info from the ab version installed on my Mac (v2.3) is listed below. As you can see there are many useful options for outputting results, and sending additional data in the request.

Usage: ab [options] [http[s]://]hostname[:port]/path
Options are:
    -n requests     Number of requests to perform
    -c concurrency  Number of multiple requests to make
    -t timelimit    Seconds to max. wait for responses
    -b windowsize   Size of TCP send/receive buffer, in bytes
    -p postfile     File containing data to POST. Remember also to set -T
    -T content-type Content-type header for POSTing, 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.
    -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.
    -h              Display usage information (this message)
    -Z ciphersuite  Specify SSL/TLS cipher suite (See openssl ciphers)
    -f protocol     Specify SSL/TLS protocol (SSL2, SSL3, TLS1, or ALL)