The high-level checklist:
- 0. Set the configuration flag to "old" (see T166732) (not needed, default is now "old")
- 1. Merge the first patch for T166732: Refactor comment storage in the database and abstract access in MediaWiki (adding new schemas and code)
- 2. Perform schema change (T174569)
- 3. Turn the feature flag to "read+write both". See if stuff breaks.
- 3.1. Announce the pending change to wikitech-l@ and cloud@, and give time for people to update.
- 3.2. Make sure all deployed extensions are updated.
- 4. Turn the feature flag to "write new only, read both". See if stuff breaks.
- 5. Run the maintenance script(s) to migrate all the old stuff to new stuff, blanking the old stuff in the process.
- 6. Turn the feature flag to "new only".
- 7. Merge the second patch for T166732 (removing old schemas and code)
- 7.1. Submit schema change (task TBD)
We can easily do steps 2–6 for individual wikis rather than rolling it out all at once. I'm filing this task now mainly so that possibility can be discussed: do we want to do that, and if so decide which wikis to do preliminary deploys to.