What happens when 200 users fill-in a survey at the same time?

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3 years 3 months ago #119502 by fransmarcelissen
fransmarcelissen created the topic: What happens when 200 users fill-in a survey at the same time?
Is there anyone who has experience with the following issue? I have often large projects with 1000+ persons who fill-in a (large) questionnaire. This does not cause any problems, because almost never more than one person go to the survey at the same time. Now I will have a project where 200 students may log-in at the same time, in a class room. Does anyone have any experience with this? May this give problems with performance and/or security?
At this moment I have a rather simple linux vps with only 1024mb ram and one core. I expect this may not be enough?

Thanks for sharing your experience and thoughts.
Frans

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3 years 3 months ago #119507 by eloner
eloner replied the topic: What happens when 200 users fill-in a survey at the same time?
I had a questionnaire (20 minutes) on a linux virtual machine with 1 core and 1 gb ram.
With 70 students logging in at the same time the system crashed.
The solution was to increase the values to 4 Gb and to 2 CPU. Further, I sent the invitations in groups of 400/500 every hour in order to have less than 100 contemporary accesses to the server.
If you use mysql, check the value of max_connection allowed to the database (by default it should be 151).
Finally, on the server you can use the commands free and top to check the amount of free memory.
I suggest to split the sample in two groups (but with only 1 Gb and 1 Cpu it might not be sufficient).
Cheers,
Elo

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3 years 3 months ago #119540 by aesteban
aesteban replied the topic: What happens when 200 users fill-in a survey at the same time?
Just to confirm eloner response. Your resources are not enough for 1000 concurrent users.

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3 years 3 months ago #119544 by fransmarcelissen
fransmarcelissen replied the topic: What happens when 200 users fill-in a survey at the same time?
Thanks for the valuable responses. I will have 200 concurrent users, not 1000. Is it reasonable to expect that two cores and 4 GB will be enough? Or should I go form 8 GB (or even higher)? Of cause more is better, but also more expensive.
Frans

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3 years 3 months ago - 3 years 3 months ago #120444 by jelo
jelo replied the topic: What happens when 200 users fill-in a survey at the same time?

Dorothy wrote: I installed it just now, good to see your valuable post before I open survey.
Is it performance defect? Mentioned not only once here.


Since Limesurvey is on top of stack (Datacenter, Hardware, OS, Webserver, Database, PHP Engine there is no simple rule of thumb. The usage of RAM is very different since a e.g. webserver can be configured in thousands of ways. How many concurrent users a system can bear is a trial and monitoring thing.

Limesurvey is weak in starting the php session, which is created for every user hitting the survey.
These session files, when written to a storage can be big. 1 MB per user is not seldom. If you are on shared hosting you can hit limits fast. But it depends on the provider and their systems.

CPU Power, Memory, IOPS of the Storage and Bandwidth are the limiting factors in term of resources. Next comes the configuration of the OS, Webserver, Datebase and PHP. This all is not related to Limesurvey. There is always room for optimization of the limesurvey codebase. But it isn't in that bade shape that your Setups should start there.

I use SSD storage for hosting surveys to reduce delay when many sessions files are written. To calculate RAM you have to know how many webserver processes can be started and how much ram one process is consuming. 4 RAM can be good, can be nothing.

But this out of scope for this forum.
Last Edit: 3 years 3 months ago by jelo.
The following user(s) said Thank You: Ben_V

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