z-Tree terminal freeze with more than 8 participants

[Ruben]

Dear Max, Matthias and Thomas,

First of all, thank you for the great software which allows me to run experiments online. I’ve installed the VM and ran several successful sessions.

However, I’ve encounter a problem: the z-Tree terminal and clients might freeze when running a session with more than approximately 8 clients.

I run z-Tree 5.1.6 with the VM installed as instructed. The structure of my experiment is as follows:

1st treatment: introduction (1 participant per treatment)

2nd treatment: 2-player game for matched subject (2 participants per treatment)

3rd treatment: payoff (1 participant per treatment)

At some point – usually when roughly 8 participants have finished the introduction and are in the second treatment - the z-Tree terminal in the VM freezes (timers stop and z-Tree is unresponsive). Participants still see their screen, but they are no longer able to press any of the buttons. After a reload (Terminate session -> reuse sessionfile -> restore session) participants can continue, but it might freeze again.

The freeze seems to occur when a participant finishes a treatment. For me, with very limited knowledge about VM’s, this might be an issue where there is too much information sent to the server. Could it be the case that I’m running too many treatments at the same time?

I’m running additional sessions on Thursday and Friday, so if you want me to collect additional information I’ll be more than happy to do so. Any help is greatly appreciated.

Kind regards,

Ruben van Oosten (Phd candidate, University of Amsterdam)

[Max R. P. Grossmann]

Hi Ruben,

What is the configuration of your VM? How many CPU cores does it have? How much RAM?

Best,

Max

[Ruben van Oosten]

Hi Max,

I'm running a VM with 4 CPUs and 18GB Base Memory (both are at maximum). The VM is installed on a rather old HP Elitebook 8570w.

Kind regards,

Ruben

[Ruben van Oosten]

Hi Max,

I think it could be a CPU issue. Ending approximately 10 treatments at the same time leads to this very high CPU usage.

Regards,

Ruben

[Max R. P. Grossmann]

Hi Ruben,

That actually looks quite ordinary, also with respect to RAM. Please see the email I sent you privately (maybe it's in the spam folder).

Best,

Max

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