refactor: address PR review feedback for column metadata optimizations

- Replace magic number 0x0015 with TypeDuration constant in readTypeInfo fast-path
- Extract duplicated keyspaceTableTracker logic in parsePreparedMetadata
- Add detailed inline comment explaining parseResultMetadata simplification

Author: mykaul

frame.go

@@ -723,8 +723,9 @@ func (f *framer) readTypeInfo() TypeInfo {
 		typ:   Type(id),
 	}
 
-	// Fast path: simple native types (0x0001-0x0015) need no further processing
-	if id > 0 && id <= 0x0015 {
+	// Fast path: simple native types (0x0001 through TypeDuration) need no further processing.
+	// These are all scalar types that require no additional wire reads beyond the type ID.
+	if id > 0 && id <= uint16(TypeDuration) {
 		return simple
 	}
 
@@ -851,23 +852,16 @@ func (f *framer) parsePreparedMetadata() preparedMetadata {
 	}
 
 	var cols []ColumnInfo
-	sameKeyspaceTable := true
-	firstKeyspace := ""
-	firstTable := ""
 	readPerColumnSpec := !globalSpec
+	var tracker keyspaceTableTracker
 	if meta.colCount < 1000 {
 		// preallocate columninfo to avoid excess copying
 		cols = make([]ColumnInfo, meta.colCount)
 		for i := 0; i < meta.colCount; i++ {
 			col := &cols[i]
 			keyspace, table := f.readColWithSpec(col, &meta.resultMetadata, globalSpec, meta.keyspace, meta.table, i, readPerColumnSpec)
 			if readPerColumnSpec {
-				if i == 0 {
-					firstKeyspace = keyspace
-					firstTable = table
-				} else if keyspace != firstKeyspace || table != firstTable {
-					sameKeyspaceTable = false
-				}
+				tracker.track(i, keyspace, table)
 			}
 		}
 	} else {
@@ -877,20 +871,15 @@ func (f *framer) parsePreparedMetadata() preparedMetadata {
 			var col ColumnInfo
 			keyspace, table := f.readColWithSpec(&col, &meta.resultMetadata, globalSpec, meta.keyspace, meta.table, i, readPerColumnSpec)
 			if readPerColumnSpec {
-				if i == 0 {
-					firstKeyspace = keyspace
-					firstTable = table
-				} else if keyspace != firstKeyspace || table != firstTable {
-					sameKeyspaceTable = false
-				}
+				tracker.track(i, keyspace, table)
 			}
 			cols = append(cols, col)
 		}
 	}
 
-	if !globalSpec && meta.colCount > 0 && sameKeyspaceTable {
-		meta.keyspace = firstKeyspace
-		meta.table = firstTable
+	if !globalSpec && meta.colCount > 0 && tracker.allSame {
+		meta.keyspace = tracker.keyspace
+		meta.table = tracker.table
 	}
 
 	meta.columns = cols
@@ -919,6 +908,24 @@ func (r resultMetadata) String() string {
 	return fmt.Sprintf("[metadata flags=0x%x paging_state=% X columns=%v]", r.flags, r.pagingState, r.columns)
 }
 
+// keyspaceTableTracker tracks whether all columns in a prepared statement
+// share the same keyspace and table, recording the first column's values.
+type keyspaceTableTracker struct {
+	keyspace string
+	table    string
+	allSame  bool
+}
+
+func (t *keyspaceTableTracker) track(colIndex int, keyspace, table string) {
+	if colIndex == 0 {
+		t.keyspace = keyspace
+		t.table = table
+		t.allSame = true
+	} else if keyspace != t.keyspace || table != t.table {
+		t.allSame = false
+	}
+}
+
 func (f *framer) readColWithSpec(col *ColumnInfo, meta *resultMetadata, globalSpec bool, keyspace, table string, colIndex int, readPerColumnSpec bool) (string, string) {
 	if readPerColumnSpec {
 		// In case of prepared statements with per-column spec, we need to read the keyspace and table for each column.
@@ -964,7 +971,12 @@ func (f *framer) parseResultMetadata() resultMetadata {
 
 	globalSpec := meta.flags&frm.FlagGlobalTableSpec == frm.FlagGlobalTableSpec
 	if globalSpec || meta.colCount > 0 {
-		// globalSpec: read from metadata position; !globalSpec: read from first column position
+		// When globalSpec is set, keyspace/table are encoded once at the metadata level.
+		// When !globalSpec, the protocol encodes keyspace/table per-column, but in practice
+		// CQL result sets always come from a single table, so we read from the first column's
+		// position and reuse for all columns. This avoids per-column string allocation.
+		// See readColWithSpec: column 0 skips reading (already consumed here), columns 1+
+		// skip the redundant per-column keyspace/table bytes on the wire.
 		meta.keyspace = f.readString()
 		meta.table = f.readString()
 	}