fix(storage): Feedback in response to PR review

* Adds clarifying documentation
* Regenerate protocol buffers with updated documentation

storage/reads/datatypes/storage_common.pb.go

@@ -987,7 +987,8 @@ func (m *TagValuesRequest) XXX_DiscardUnknown() {
 
 var xxx_messageInfo_TagValuesRequest proto.InternalMessageInfo
 
-// Response message for Storage.TagKeys and Storage.TagValues.
+// Response message for Storage.TagKeys, Storage.TagValues Storage.MeasurementNames,
+// Storage.MeasurementTagKeys and Storage.MeasurementTagValues.
 type StringValuesResponse struct {
 	Values [][]byte `protobuf:"bytes,1,rep,name=values,proto3" json:"values,omitempty"`
 }
@@ -1188,6 +1189,7 @@ func (m *MeasurementFieldsRequest) XXX_DiscardUnknown() {
 
 var xxx_messageInfo_MeasurementFieldsRequest proto.InternalMessageInfo
 
+// MeasurementFieldsResponse is the response message for Storage.MeasurementFields.
 type MeasurementFieldsResponse struct {
 	Fields []MeasurementFieldsResponse_MessageField `protobuf:"bytes,1,rep,name=fields,proto3" json:"fields"`
 }

storage/reads/datatypes/storage_common.proto

@@ -174,7 +174,8 @@ message TagValuesRequest {
   string tag_key = 4;
 }
 
-// Response message for Storage.TagKeys and Storage.TagValues.
+// Response message for Storage.TagKeys, Storage.TagValues Storage.MeasurementNames,
+// Storage.MeasurementTagKeys and Storage.MeasurementTagValues.
 message StringValuesResponse {
   repeated bytes values = 1;
 }
@@ -210,6 +211,7 @@ message MeasurementFieldsRequest {
   Predicate predicate = 4;
 }
 
+// MeasurementFieldsResponse is the response message for Storage.MeasurementFields.
 message MeasurementFieldsResponse {
   enum FieldType {
     option (gogoproto.goproto_enum_prefix) = false;

tsdb/cursors/schema.go

@@ -27,19 +27,20 @@ var (
 	}
 )
 
-// IsLower returns true if the other FieldType has greater precedence than the
-// current value. Undefined has the lowest precedence.
-func (ft FieldType) IsLower(other FieldType) bool { return other < ft }
-
-// FieldTypeToDataType returns the equivalent influxql DataType for the field type ft
+// FieldTypeToDataType returns the equivalent influxql DataType for the field type ft.
+// If ft is an invalid FieldType, the results are undefined.
 func FieldTypeToDataType(ft FieldType) influxql.DataType {
 	return fieldTypeToDataTypeMapping[ft&7]
 }
 
+// IsLower returns true if the other FieldType has greater precedence than the
+// current value. Undefined has the lowest precedence.
+func (ft FieldType) IsLower(other FieldType) bool { return other < ft }
+
 type MeasurementField struct {
-	Key       string
-	Type      FieldType
-	Timestamp int64
+	Key       string    // Key is the name of the field
+	Type      FieldType // Type is field type
+	Timestamp int64     // Timestamp refers to the maximum timestamp observed for the given field
 }
 
 // MeasurementFieldSlice implements sort.Interface and sorts