Exceeding Interview Variables size limit

Question

Dear SoSci support,

After creating a survey, we get the following error as shown in the error log file:

[03-May-2021 15:14:07 Europe/Berlin] Verbose: Exceeding overall variable (65579 bytes) for InterviewVariable in P=60/C=711, new variable: history
[03-May-2021 15:14:09 Europe/Berlin] Verbose: Exceeding overall variable (65579 bytes) for InterviewVariable in P=60/C=711, new variable: history
[03-May-2021 15:14:11 Europe/Berlin] Verbose: Exceeding overall variable (65579 bytes) for InterviewVariable in P=60/C=711, new variable: history
[03-May-2021 15:14:14 Europe/Berlin] Verbose: Exceeding overall variable (65579 bytes) for InterviewVariable in P=60/C=711, new variable: history

Do you know which causes it?

We tried to debug it without success.
In the SoSci Survey PHP code, we found the following:

'InterviewVariables.size limit' => 'Adding the entry for %name% the data stored in this interview would exceed the limit of 64 KB. The value for %name% could therefore not be saved. This may cause errors in the questionnaire, the questionnaire may stop here, for example.'

What does this limit refer to? It would be very useful for us to know what exactly this limit refers to, to try to fix the issue.

Thank you very much for your help.
Best regards,

Answer 1

There is several metadata stored for each interview. This incluce

• the "history" that stored which pages have been displaed and which numbers the questions had on these pages
• variables registered via registerVariable()
• page orders set via setPageOrder(), loopPage(), loopToPage() and setNextPage()
• item-rotation of quesions

Overall, there is a limit of 64 kilobytes for this data per interview case. If you exceed that, the issue very often lies within page orders. More specifically: pages within a loop that do not display content and are skipped. This diplucates the amount that this page order requires with each skipped page.

Often it's sufficient to put the contents (usually PHP code) from a page that is skipped onto the next or previous page, and remove that page.

The numbers in the error message are the project's ID and the case number. So it seems that all the error messages stem from case 711 in project 60.