1. ALTERs to run:

ALTER TABLE /*_*/globalblocks
  CHANGE gb_by_wiki gb_by_wiki VARBINARY(255) NOT NULL;

1. Where to run those changes: centralauth DB
2. When to run those changes: When DBA has time, very low priority
3. If the schema change is backwards compatible: Yes
4. If the schema change has been tested already on some of the test/beta wikis: The beta wikis do not have a default set for gb_by_wiki
5. If the data should be made available on the labs replicas and/or dumps: Yes, no changes to existing rules needed

As detailed in T381502: Fix GlobalBlocking database schema drifts in production, the gb_by_wiki column has a default set on WMF wikis but the GlobalBlocking extension schema has this without a default set. Looking further, it seems that there was no default set in the SQL that was defined before the conversion to an abstract schema, so it seems that we shouldn't need a patch to GlobalBlocking to address this.

Acceptance criteria

• The default value on gb_by_wiki is removed from the globalblocks table on the centralauth DB