问题
I'm load testing an API. We have a problem - our response times are too large, sometimes close to a minute. We want to be at the range of under a second. But that is besides the point.
When I use a load testing tool, such as Gatling, the RPS sent seem to hit a halt. As you can see in the attached image, there is an initial 15 seconds of 20RPS, and suddenly almost no RPS at all. How can I maintain constant RPS? Probably it has to do with the poor response times, but what if I don't care about the response times? I just want the RPS constant.
My initial tests with JMeter also show similar behaviour.
回答1:
What injection strategy are you using? How scenario looks? Is every user making one request, chain of requests or any of above in a loop?
Assuming that you want to test single endpoint, best approach to get constant requests per second (not constant responses as you already know) is to use scenario that executes single request and strategy that injects constant number of users per second fe:
setUp(
scn.inject(constantUsersPerSec(25) during(15 minute))
)
If your user performs more then 1 requests there is option to throttle requests, but you need to remember that it will only throttle down not up, so you need to make sure that active users will make enough requests per second to reach that limit fe:
setUp(scn.inject(
constantUsersPerSec(10) during(15 minutes)
).throttle(
jumpToRps(25), holdFor(15 minutes)
))
So here if fe. single user makes 5 requests you can reach even 50 req/s but it will be throttled to 25. But you must remember that new users will be added every second so if it takes more time to finish 1 user then number of active users will increase. Also if response time is high then active users may not produce enough req/s since most of their time is waiting for response.
回答2:
In JMeter, You can achieve that by using Constant Throughput Timer at your test plan level.
Constant Throughput timer allows you to maintain the throughput of your server (requests/sec). Constant Throughput Timer is only capable of pausing JMeter threads in order to slow them down to reach the target throughput. Also, it works only on a minute level so you need to properly calculate the ramp-up period and let your test run long enough.
Let's see a brief thought on this:
To achieve the target throughput, you need to have enough number of threads in your test plan.
To calculate the number of threads you need for this test, you can use the below formula:
RPS * max response time in second
In your case, If you want 20 RPS and your max response time is 60 seconds, you need at least 1200 (20*60=1200) Threads in your test plan.
As Constant Throughput Timer works on a minute level, to achieve 20 RPS you have to configure your "Target Throughput" value to 1200/min and "Calculate Throughput based on" value as "All active threads".
Constant Throughput Timer Config:
Now, if you have more than single requests in your test plan (i.e 4 requests), then 1200 requests/min will be distributed among 4 samplers. That means you will get 5RPS for each sampler.
Now, for the Thread Group configurations, as you have mentioned "Calculate Throughput based on" value in Constant Throughput Timer for "All active threads", so all of your 1200 threads need to be started on the server to achieve that 20 RPS. Use Ramp-Up Period config to control these threads to start.
Ramp-Up Period is the time in which all the threads arrive on your tested application server. So if you use 60 seconds, then it will take 60 seconds to start all of your 1200 threads. 1200 threads will be active in 60 seconds.
You also need to set your test duration accordingly. Say, you want to keep that 20 RPS for 5 minutes. In this case, you have to set your test duration for 7 mins (2 min extra is for: Starting 1 min for 1200 threads to start which is the ramp up time and last 1 min for the 1200 threads ramp-down time). Don't forget to check the loop counts to Forever if you are using Thread Group.
Thread Group Config for the above-mentioned scenario:
You can also use another handy JMeter plugin which is Ultimate Thread Group if you are confused with the default Thread Group configurations. You can download JMeter Plugins by using JMeter Plugins Manager.
Here is the Ultimate Thread Group Config for the above-mentioned scenario:
Now while after the test finishes, you can check those 5 minutes results where all of your 1200 threads were active by using the Hits Per Second Listener and as well as Active Threads Over Time Listener.
Do not use JMeter GUI for Load testing, use the Non-GUI mode. Also, remove assertions if you have any in your test plan while you're trying to achieve some target RPS.
来源：https://stackoverflow.com/questions/55136069/gatling-and-jmeter-struggling-to-maintain-requests-per-second-rps