Benchmarking Your Site with `http_load`

Sunday, January 28, 2007

http_load is a stunningly useful HTTP benchmarking utility that gives you a rough idea of how many hits per second a server is capable of serving. You simply tell it what pages to grab, and how many “clients” it should run in parallel; it gives you back useful information about the average fetches per second and the average, minimum, and maximum response times. It’s no substitute for a solid profiler to dig into the hows and whys of your application’s performance, but it’s great at telling you when you’re “good enough” to launch.

Installing `http_load` on OS X

Installation is not tough, it’s the typical make, then make install process that you’ll use just about any time you install a *nix application from source. It even defaults to /usr/local/bin, perfect.

So, here we go:

mkdir ~/http_load_src
cd ~/http_load_src
curl -O http://www.acme.com/software/http_load/http_load-12mar2006.tar.gz
tar -xzvf ./http_load-12mar2006.tar.gz
cd http_load-12mar2006
make
sudo make install
cd ~
rm -rf ~/http_load_src

You’ll end up with the application installed at /usr/local/bin/http_load, and if you’ve set your PATH to include /usr/local, then you’re good to go.

Using `http_load` to Benchmark Your Site

Once installed, using http_load for quick benchmarking is really quite straightforward. You call the program, tell it how many requests to make concurrently, and how long to run (either in number of seconds, or total fetches), and finally pass in a file full of URLs to request.

To see how many requests your server can take care of over a 5 second period, run:

http_load -parallel 10 -seconds 5 ./omg_its_full_of_urls.txt

You’ll get back a response that looks something like:

3587 fetches, 10 max parallel, 6.97698e+06 bytes, in 5.00052 seconds
1945.07 mean bytes/connection
717.325 fetches/sec, 1.39525e+06 bytes/sec
msecs/connect: 0.674328 mean, 20.771 max, 0.045 min
msecs/first-response: 12.4517 mean, 389.405 max, 1.978 min
HTTP response codes:
  code 200 -- 3587

The numbers you’ll want to look at in more detail are “fetches/sec” and “msecs/first-response”. These are critical in terms of really understanding what your site is doing.

It’s important to note the difference between “benchmarking” and “profiling”. What we’re doing here with http_load is the former: we’re getting a feel for a specific page’s overall performance. We know that it serves X pages per second, and generally takes about Y milliseconds to response. What we don’t know yet is why either of these is the case. You’ll have to dig in more detail into your PHP code and server configuration to determine what to tweak to bring up your site’s performance to an acceptable level. http_load doesn’t, and can’t, do that for you.

A Tip for Shell Scripters

Generally speaking, I’m only testing one URL at a time to determine the performance of a specific script on a site. For this case, creating a file with a single URL inside is a little annoying, so I whipped up a quick bash script to make it happen for me. Add the following function to your .bash_profile, and you can simply type “httpload [url] [clients] [seconds]” to run a quick benchmark.

httpload() {
    STAMP=`date +"%s"`;
    echo "http://$1" > /var/tmp/$STAMP.http_load_temp_file
    http_load -parallel $2 -seconds $3 /var/tmp/$STAMP.http_load_temp_file
    rm -f /var/tmp/$STAMP.http_load_temp_file
}

Hooray for bash scripting!

Troubleshooting

It looks like Leopard introduces some quirks to the process. If you’re getting an error like:

rm -f /usr/local/bin/http_load
cp http_load /usr/local/bin
rm -f /usr/local/man/man1/http_load.1
cp http_load.1 /usr/local/man/man1
cp: /usr/local/man/man1: No such file or directory
make: *** [install] Error 1

Then do the following to fix up the problem:

sudo rm /usr/local/bin
sudo mkdir -p /usr/local/bin/
sudo mkdir -p /usr/local/share/man/man1/
sudo ln -s /usr/local/share/man/ /usr/local/man
make clean
make
sudo make install

In a nutshell, Leopard doesn’t come with a /usr/local/bin directory, and seems to have moved the location of local manual pages from /usr/local/man/ to /usr/local/share/man/`. The commands above will create the binary and manual page directories you’ll need, and sets up a symlink mapping the old directory structure to the new one.

Magic!

— Mike West