code: public void addFieldReferences(TableDefinition tableDef, Collection<String> fieldNames) {
          for (String fieldName : fieldNames) {
              addColumn(SpiderService.termsStoreName(tableDef), FIELD_REGISTRY_ROW_KEY, fieldName);
          }
      }
docs: Add a column to the "_fields" row belonging to the given table for the given scalar
  field names. This row serves as a registry of scalar fields actually used by objects
  in the table. Field references go in the Terms table using the format:
  <pre>
  _fields = {{field 1}:null, {field 2}:null, ...}
  </pre>
  
  @param tableDef      Table that owns referenced fields.
  @param fieldNames    Scalar field names that received an update in the current
  transaction.