The ALTER TABLES to run: https://gerrit.wikimedia.org/r/#/c/271435/5/maintenance/archives/patch-watchlist-wl_id.sql
Where to run those changes: All mediawiki dbs
When to run those changes: ASAP
If the schema change is backwards compatible: compatible with the current code deployed.
If the schema change has been tested already on some of the test/beta wikis. Usually, as a last test, change should be applied
to testwiki first: We will be testing on Labs, Beta and testwiki (along with deployment). Nothing actually uses the id field yet so this basically should be a noop
If it involves new columns or tables, if the data should be made available on the labs replicas. Similar question if it involves deletion of data previously available on labs. YES
**Status as of 2017-04-27:** Done on eqiad, pending on codfw. Do not deploy any code based on it yet.