Disable Custom Variables feature by default #11524

We need to deprecate Custom Variables in favor of Custom Dimensions.

In Piwik 4, maybe we could deactivate the CustomVariables plugin, if no Custom Variable has been tracked so far in this Piwik?

Additionally we would need to find ways to promote the Custom Dimensions feature within the product. By showing some ads or notifications in some way.

Thoughts?

Sounds good. I reckon in general it will be a hard transition to get rid of it in terms of providing a good experience to users who still use it. We could for sure mention it in Custom Variables report etc.

Also what about custom variables in scope event?

@tsteur AFAIK the same benefits can be achieved with custom dimensions on events?

Ideas so far for Custom Variables deprecation

• display a message below Custom Variables reports, where we recommend to use Custom Dimensions instead
• in Piwik 4, for new installations, do not enable Custom Variables
• in Piwik 4, for users upgrading, possibly we can detect whether any custom variable has been used so far in this Piwik server, and if never used, disable the plugin automatically
• possibly we can go as far as removing the source code from Piwik release package, and move this plugin to the Marketplace?

Before we can disable custom variables in core, we need to change any core features which currently use Custom Variables (all of it is "hacky"):

• Ecommerce view tracking uses custom variables, which leads to bugs such as https://github.com/piwik/piwik/issues/12035 -> we should rewrite Ecommerce tracking to work without custom variables.
• Custom vars also used in the Log Importer to
  • set Http-Status codes,
  • whether the user is a bot or not,
  • track the HTTP method GET VS POST
  • etc.
    This would need some adjustements (refs)
• Custom variables also used for Site Search tracking, implementation should be rewritten see #12072

The Log Analytics conversion work is well underway in https://github.com/matomo-org/matomo-log-analytics/pull/214 :+1:

Another thing i noticed:

• in the following config settings should be renamed (of course with BC kept)

  datatable_archiving_maximum_rows_custom_variables = 5000
  datatable_archiving_maximum_rows_subtable_custom_variables = 5000