CODEWITHSUNDEEP
performanceperformance-testingapachebench
glaz666
glaz666

Reputation: 8721

Different results in ApacheBench with and without concurrent requests

I am trying to get some statistics on response time at my production server.

When calling ab -n100 -c1 "http://example.com/search?q=something" I get following results:

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       24   25   0.7     24      29
Processing:   526  874 116.1    868    1263
Waiting:      313  608 105.1    596    1032
Total:        552  898 116.1    892    1288

But when I call ab -n100 -c3 "http://example.com/search?q=something" the results are much worse:

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:       24   25   0.8     25      30
Processing:   898 1872 1065.6   1689    8114
Waiting:      654 1410 765.5   1299    7821
Total:        923 1897 1065.5   1714    8138

Taking into account that site is in production, so there are requests besides mine, I can't explain why call with no concurrency are so much faster than with even small concurrency.

Any suggestions?

Upvotes: 1

Views: 828

Answers (1)

Oliver Lloyd
Oliver Lloyd

Reputation: 5004

If you have a concurrency of 1 that means you are telling AB to hit this URL, as fast as it can, using one thread. The value -c3 is telling AB to do the same thing but using 3 threads which is probably going to result in a greater volume of calls which, in your case, appears to have caused things to slow down. (Note AB is single-threaded so doesn't actually use multiple os threads but the analogy still holds true.)

It's a bit like having more lanes at the tollbooth, one lane can only process cars so fast but with three lanes you're going to get more throughput. But no matter how many lanes you have the width of the tunnel the cars have to pass through after the tollbooth is also going to affect throughput which is probably what you are seeing.

As a general note, a better approach to load testing is to decide what level of traffic your app needs to be able to support and then design a test that generates this level of throughput and no more. Running threads as fast as they can like AB does tends to make any kind of controlled testing hard. JMeter is better.

Also, you might want to think about setting up a test server for his sort of thing, less risky...

Upvotes: 1

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