Should cover the journey a Wikidata edit becomes a RC change in RC table on Wikipedia.
Some of this is covered in text form in https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/master/docs/topics/usagetracking.md and https://github.com/wikimedia/mediawiki-extensions-Wikibase/blob/master/docs/topics/usagetracking-migration.md . The rest of the information needs to be gleaned by reading the source code for jobs. There are multiple TODOs on this topic in the code.
The data flow diagram should capture the following:
- Data stores such as database and especially intermediate caches.
- Processes that move the data (data stores should always be connected by a process), these will mostly be background jobs.
- Type of data moving along the flow lines.
- In particular, where the decision is made of what kind of change it is
Recommended to write the diagram as Mermaid blocks in the markdown documentation.
The scalability issues could be illustrated with a deployment diagram.