ab load testing

The apache benchmark tool is very basic, and while it will give you a solid idea of some performance, it is a bad idea to only depend on it if you plan to have your site exposed to serious stress in production.

Having said that, here's the most common and simplest parameters:

-c: ("Concurrency"). Indicates how many clients (people/users) will be hitting the site at the same time. While ab runs, there will be -c clients hitting the site. This is what actually decides the amount of stress your site will suffer during the benchmark.

-n: Indicates how many requests are going to be made. This just decides the length of the benchmark. A high -n value with a -c value that your server can support is a good idea to ensure that things don't break under sustained stress: it's not the same to support stress for 5 seconds than for 5 hours.

-k: This does the "KeepAlive" funcionality browsers do by nature. You don't need to pass a value for -k as it it "boolean" (meaning: it indicates that you desire for your test to use the Keep Alive header from HTTP and sustain the connection). Since browsers do this and you're likely to want to simulate the stress and flow that your site will have from browsers, it is recommended you do a benchmark with this.

The final argument is simply the host. By default it will hit http:// protocol if you don't specify it.

ab -k -c 350 -n 20000 example.com/

By issuing the command above, you will be hitting http://example.com/ with 350 simultaneous connections until 20 thousand requests are met. It will be done using the keep alive header.

After the process finishes the 20 thousand requests, you will receive feedback on stats. This will tell you how well the site performed under the stress you put it when using the parameters above.

For finding out how many people the site can handle at the same time, just see if the response times (means, min and max response times, failed requests, etc) are numbers your site can accept (different sites might desire different speeds). You can run the tool with different -c values until you hit the spot where you say "If I increase it, it starts to get failed requests and it breaks".

Depending on your website, you will expect an average number of requests per minute. This varies so much, you won't be able to simulate this with ab. However, think about it this way: If your average user will be hitting 5 requests per minute and the average response time that you find valid is 2 seconds, that means that 10 seconds out of a minute 1 user will be on requests, meaning only 1/6 of the time it will be hitting the site. This also means that if you have 6 users hitting the site with ab simultaneously, you are likely to have 36 users in simulation, even though your concurrency level (-c) is only 6.

This depends on the behavior you expect from your users using the site, but you can get it from "I expect my user to hit X requests per minute and I consider an average response time valid if it is 2 seconds". Then just modify your -c level until you are hitting 2 seconds of average response time (but make sure the max response time and stddev is still valid) and see how big you can make -c.

I hope I explained this clear :) Good luck

Please walk me through the commands I should run to figure this out.

The simplest test you can do is to perform 1000 requests, 10 at a time (which approximately simulates 10 concurrent users getting 100 pages each - over the length of the test).

ab -n 1000 -c 10 -k -H "Accept-Encoding: gzip, deflate" http://www.example.com/

-n 1000 is the number of requests to make.

-c 10 tells AB to do 10 requests at a time, instead of 1 request at a time, to better simulate concurrent visitors (vs. sequential visitors).

-k sends the KeepAlive header, which asks the web server to not shut down the connection after each request is done, but to instead keep reusing it.

I'm also sending the extra header Accept-Encoding: gzip, deflate because mod_deflate is almost always used to compress the text/html output 25%-75% - the effects of which should not be dismissed due to it's impact on the overall performance of the web server (i.e., can transfer 2x the data in the same amount of time, etc).

Results:

Benchmarking www.example.com (be patient)
Completed 100 requests
...
Finished 1000 requests


Server Software:        Apache/2.4.10
Server Hostname:        www.example.com
Server Port:            80

Document Path:          /
Document Length:        428 bytes

Concurrency Level:      10
Time taken for tests:   1.420 seconds
Complete requests:      1000
Failed requests:        0
Keep-Alive requests:    995
Total transferred:      723778 bytes
HTML transferred:       428000 bytes
Requests per second:    704.23 [#/sec] (mean)
Time per request:       14.200 [ms] (mean)
Time per request:       1.420 [ms] (mean, across all concurrent requests)
Transfer rate:          497.76 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.1      0       1
Processing:     5   14   7.5     12      77
Waiting:        5   14   7.5     12      77
Total:          5   14   7.5     12      77

Percentage of the requests served within a certain time (ms)
  50%     12
  66%     14
  75%     15
  80%     16
  90%     24
  95%     29
  98%     36
  99%     41
 100%     77 (longest request)

For the simplest interpretation, ignore everything BUT this line:

Requests per second:    704.23 [#/sec] (mean)

Multiply that by 60, and you have your requests per minute.

To get real world results, you'll want to test Wordpress instead of some static HTML or index.php file because you need to know how everything performs together: including complex PHP code, and multiple MySQL queries...

For example here is the results of testing a fresh install of Wordpress on the same system and WAMP environment (I'm using WampDeveloper, but there are also Xampp, WampServer, and others)...

Requests per second:    18.68 [#/sec] (mean)

That's 37x slower now!

After the load test, there are a number of things you can do to improve the overall performance (Requests Per Second), and also make the web server more stable under greater load (e.g., increasing the -n and the -c tends to crash Apache), that you can read about here:

Load Testing Apache with AB (Apache Bench)

Steps to set up Apache Bench(AB) on windows (IMO - Recommended).

Step 1 - Install Xampp.
Step 2 - Open CMD.
Step 3 - Go to the apache bench destination (cd C:\xampp\apache\bin) from CMD
Step 4 - Paste the command (ab -n 100 -c 10 -k -H "Accept-Encoding: gzip, deflate" http://localhost:yourport/)
Step 5 - Wait for it. Your done

Load testing your API by using just ab is not enough. However, I think it's a great tool to give you a basic idea how your site is performant.

If you want to use the ab command in to test multiple API endpoints, with different data, all at the same time in background, you need to use "nohup" command. It runs any command even when you close the terminal.

I wrote a simple script that automates the whole process, feel free to use it: http://blog.ikvasnica.com/entry/load-test-multiple-api-endpoints-concurrently-use-this-simple-shell-script