ExpectedDescriptorIDs returns the list of all expected system descriptor IDs, including those added by completed migrations.

NewManager initializes and returns a new Manager object.

SettingsDefaultOverrides documents the effect of several migrations that add an explicit value for a setting, effectively changing the "default value" from what was defined in code.

Manager encapsulates the necessary functionality for handling migrations of data in the cluster.

MigrationManagerTestingKnobs contains testing knobs.