verifyOrCreateDvOnlyField
This function is called from IndexWriter to verify if doc values of the field can be updated. If the field with this name already exists, we verify that it is a doc values-only field. If the field doesn't exist and the parameter fieldMustExist is false, we create a new field in the global field numbers.
Parameters
fieldName
name of the field
dvType
expected doc values type
fieldMustExist
– if the field must exist.
Throws
if the field must exist, but it doesn't, or if the field exists, but it is not doc values only field with the provided doc values type.