T85414#4597677 details the current differences between the Wikibase DB schema as written in code and deployed to the WMF.
The wb_terms_entity_id index is in production on the wb_terms table but is not created when you install Wikibase.
Details of the index can be seen in T85414#4597677
Priority & Impact
Having differing schema between WMF production and what we use elsewhere and in development causes outages like the tmp1 outage.
The tmp1 index caused a massive outage, we want to avoid doing that in the future.
This task is small and should be easy to complete so lets get it done and avoid it sitting here for a year, at which point we may have forgotten about the hardships that it caused.
- Wikibase users upgrading from a version prior to this patch will have the index added
- Wikibase users installing a fresh install will have the index
- The index should appear exactly as it does in WMF production