Pete Freitag Pete Freitag

Use Apache Benchmark for Easy Load Testing

Updated on December 07, 2023
By Pete Freitag

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 Benchmarking tool, or ab, and even sometimes just called Apache Bench. If you are on windows and have Apache installed, you may also have ab.exe in your apache/bin folder.

Apache Benchmark Simple Example

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

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 for loop and a time stamp 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 Apache Benchmark, or ab supports concurrency, this has two big advantages over simple looping or iteration tests. 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.

Testing Multiple URLS Concurrently

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:


ab -n 100 -c 10 > test1.txt &
ab -n 100 -c 10 > test2.txt &

Apache Benchmark Options

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
Option Description
-n requests The total number of requests to make
-c concurrency Number of requests to make at the same time, or concurrently.
-t timelimit Time limit in seconds, the maximum amount of time the benchmark can take
-s timeout Time in seconds to wait for each request, the default is 30 seconds.
-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 Prints additional or verbose information.
-w Outputs the results in HTML tables
-i Use HEAD instead of GET
-m method The HTTP method to use for the requests.
-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. JSESSIONID=1234. You can repeat this option as many times as you need to.
-H attribute Add a HTTP request header line, eg. 'Accept-Encoding: gzip' Inserted after all normal header lines. You can repeat this argument as many times as you need to.
-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 Enable the HTTP KeepAlive feature
-d Omit the percentiles served table.
-S Omit confidence estimators and warnings.
-g filename Output collected data to gnuplot format file.
-e filename Output the results as a CSV file with percentages served
-r Don't exit on socket receive errors.
-h Display help or usage information
-Z ciphersuite Specify SSL/TLS cipher suite (See openssl ciphers)
-f protocol Specify SSL/TLS protocol (SSL2, SSL3, TLS1, TLS1.1, TLS1.2 or ALL). Depending on the version of the tool and the version of openssl you have the choices may differ.
-E certfile Specify an optional client certificate chain and private key if necessary to connect to your server.

As you can see the apache benchmark tool is pretty powerful, it doesn't have quite as many options as curl, but it can do a lot.

Where is the ab located on a Mac?

Currently you can find the ab binary at the path: /usr/sbin/ab

SSL Not compiled in; no https support

If you see the error message:

SSL Not compiled in; no https support

If you are on Windows try using the abs.exe instead of the ab.exe executable for https support on Apache Bench. I believe you may also see that error message on some older versions of the Mac binary as well. I can confirm as of at least Mac OSX Monterey (12.6) the ab binary does include support for https by default.

ab apache load testing benchmarking http concurrency

Use Apache Benchmark for Easy Load Testing was first published on February 05, 2009.

If you like reading about ab, apache, load, testing, benchmarking, http, or concurrency then you might also like:

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