In Piwik reports are processed based using the raw data. Once an archive has been processed for a website and a specific date period, and stored in the database (during the core:archive process), it can only be invalidated (via HTTP API or CLI or InvalidateReports plugin) which will force all plugins to re-process all their respective reports in the next archiving process. This is problematic because it can take a lot of time to reprocess previous reports for 3 or 12 months.

-> Plugins should be able to easily create their own reports for some of the historical data. this is useful for all plugins which don't create new raw data but re-uses the existing raw data. For example, Funnels plugin would like to process Funnels data in the past 6 months.

To make it possible for any plugin to append their reports to the existing archives, we need to make some changes to the archiving process.

Ideas:

• Piwik core to allow an existing archive to be modified later-on so new plugin's reports can be part of and appended in the existing old archive
• Piwik core to allow each plugin to force re-processing of past data and the ability to specify how far back the data should be re-processed. (working for our two use cases: when using the core:archive console command in a cron, or when using broworser triggered archiving and looking at historical data.)

(not related but a bit similar to #7573 )