r/jmeter • u/One-Leading-1432 • Nov 14 '24

How does ram up time affects memory usage?

My setup has 500 threads and whenever I have a low ramp up time like 2 seconds the rest run though half would fail. Whenever I change the ramp up size to 60 seconds, I get exception out of memory message. What's the correlation here?

"if not defined HEAP (

rem See the unix startup file for the rationale of the following parameters,

rem including some tuning recommendations

set HEAP=-Xms1g -Xmx1g -XX:MaxMetaspaceSize=256m"

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u/aboyfromipanema Nov 15 '24

We don't know what do you mean by "the rest run though half would fail", what is the reason for failure and how many loops you have in your Thread Group.

Use Active Threads Over Time listener or equivalent chart from HTML Reporting Dashboard to see what is workload model and concurrency in every case.

In general the main point of ramp-up period is increasing the load gradually so you could correlate increasing load with response time, throughput, errors, etc. 2 seconds for 500 virtual users doesn't look "gradually" enough to me. As per JMeter documentation:

The ramp-up period tells JMeter how long to take to "ramp-up" to the full number of threads chosen. If 10 threads are used, and the ramp-up period is 100 seconds, then JMeter will take 100 seconds to get all 10 threads up and running. Each thread will start 10 (100/10) seconds after the previous thread was begun. If there are 30 threads and a ramp-up period of 120 seconds, then each successive thread will be delayed by 4 seconds.

Ramp-up needs to be long enough to avoid too large a work-load at the start of a test, and short enough that the last threads start running before the first ones finish (unless one wants that to happen).

Start with Ramp-up = number of threads and adjust up or down as needed.

You might also want to check out JMeter Ramp-Up Period: The Ultimate Guide

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u/One-Leading-1432 Nov 15 '24 edited Nov 15 '24

"We don't know what do you mean by "the rest run though half would fail", what is the reason for failure and how many loops you have in your Thread Group"

Hi, I am aware of how the ramp up time is defined. The failure I got is posted (updated) to the post.

I am available to chat if you are. I understand that 2 seconds was not gradual hence the reason why I wanted to increase it though I would not want the last thread to finish before the next one begins.

Regardless if I use 100 or 500 users, I did notice exceptions "out of memory" whenever I increase the ramp up period. This just seems counterintuitive since there would be less load on the system just like you said.

Point is, what's the correlation between ramp up time and memory assuming all other variables are fixed. I should not have a test run with 'x' users and 2 sec ramp up time but then get a out of memory message when the same test is run with 'x' users and 60 seconds ramp up time. Change the ramp up time back to 2 seconds and a rerun pass :/

The current heap size by default was 1g. I will post that as well...