Measuring Performance

Whenever you attempt to make a tweak to your systems performance you need to know what result you've achieved, if any.

The best way to do that is to use a tool to test your servers performance, or throughput, and run that both before and after making any particular change.

There are several benchmarking applications and tools out there, and this small page contains a list of the ones you're most likely to need to use.

Webserver Stress-Testing

Webserver benchmarking largely consists of firing off a few thousand requests at a server, and reporting on the min/max/average response time.

Obviously a server "loses points" if some of the response are errors, rather than valid results, but generally the testing is a matter of juggling the number of total requests, or concurrent requests, until you reach a point where the server starts to take too long to respond, or fails completely.

ab

One of the most popular tools for benchmarking for many years was ab, the Apache benchmark tool. This is looking a little dated now, but still works well.

If you're running Apache you probably have this installed already, which explains its popularity. Give it a URL, a number of requests, and a concurrency level and it will issue a small report:

ab -c 10 -n 1000 http://example.com/

The example above fired 1000 requests, with 10 at a time, to the URL http://example.com/ and the results for me look something like this:

Concurrency Level:      10
Time taken for tests:   36.496 seconds
Complete requests:      1000
Failed requests:        0
Write errors:           0
Total transferred:      1610000 bytes
HTML transferred:       1270000 bytes
Requests per second:    27.40 [#/sec] (mean)
Time per request:       364.955 [ms] (mean)
Time per request:       36.496 [ms] (mean, across all concurrent requests)
Transfer rate:          43.08 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:      179  182   1.3    182     192
Processing:   182  183   1.2    182     195
Waiting:      181  183   1.2    182     195
Total:        361  364   1.9    364     383

siege

Siege is very similar to the Apache benchmark application, and allows you to request a lot of URLs from a text-file, along with other options.

A simple example might be to test a server with 50 concurrent users, and a delay of a random amount, up to 10 seconds, between requests:

siege -d10 -c50 -t60s http://example.com/

The use of -t60s will cause the testing to cease after a minute. If you were testing a large site you will probably wish to run for a lot longer.

Perhaps a more realistic approach is to save a list of URLs to the file ~/urls.txt, and fire requests from that file, randomly:

siege -d10 -c50 -t60s -i -f ~/urls.txt

In either case we'd expect to see output like this:

Transactions:                442 hits
Availability:             100.00 %
Elapsed time:              59.43 secs
Data transferred:           0.54 MB
Response time:              0.37 secs
Transaction rate:           7.44 trans/sec
Throughput:             0.01 MB/sec
Concurrency:                2.72
Successful transactions:         442
Failed transactions:               0
Longest transaction:            0.40
Shortest transaction:           0.36

Online services

There are several online testing sites which you can use to graph your server response time, these should have the advantage that you're not limited by your personal upload-speed.

As many require subscriptions, or validation, they're not suitable for all, but as an alternative to testing yourself they can be useful:

Simpler testing will just test a single page and report the time taken to load all associated resources (CSS, images, etc). Not quite as valuable, but interesting nonetheless:

Optimizing

Testing