There's no formal Schema-change here, since simply adding tables isn't classified as a schema change at https://wikitech.wikimedia.org/wiki/Schema_changes#What_is_not_a_schema_change. But we still need to make them visible in Toolforge and possibly dumps.
There are four new tables added in rMW943c724198f1: MCR database schema.
- slot_roles can be exposed without restriction.
- content_models can be exposed without restriction.
- slots will need some filtering to match the existing behavior for revision.
- The slot_content_id column should be nulled if the corresponding revision table row (join on rev_id = slot_revision_id) has rev_deleted & 1, or if the corresponding archive table row (join on ar_rev_id = slot_revision_id) has ar_deleted & 1
- content will also need some filtering to match the existing behavior for revision.
- A row should be hidden entirely if there is no row in slots that publicly refers to it (join on content_id = slot_content_id). You'll probably want to add an index on slot_content_id to be able to efficiently check this.
- We don't currently expose anything equivalent to content_address at all. It roughly corresponds to the text table's old_text when old_flags contains external (unlike the text table, there's no provision for storing actual revision content here).
See also T174047: Hide deprecated/unused fields on toolforge replica [MCR], which is about providing views that pretend fields that are being removed or replaced in MCR still exist.