Add comments and change addTables signature

level_handler.go

@@ -140,7 +140,12 @@ func (s *levelHandler) replaceTables(toDel, toAdd []*table.Table) error {
 	return decrRefs(toDel)
 }
 
-func (s *levelHandler) addTables(toAdd []*table.Table) error {
+// addTable adds toAdd tables to levelHandler. Normally when we add tables to levelHandler, we sort
+// tables based on table.Smallest. This is required for correctness of the system. But in some cases
+// this can be avoided(such as stream writer). We can just add tables to levelHandler's table list
+// and after all addTables calls, we can sort table list(check sortTable method).
+// NOTE: addTables and sortTables duplicate some code from replaceTables().
+func (s *levelHandler) addTables(toAdd []*table.Table) {
 	s.Lock()
 	defer s.Unlock()
 
@@ -150,10 +155,9 @@ func (s *levelHandler) addTables(toAdd []*table.Table) error {
 		t.IncrRef()
 		s.tables = append(s.tables, t)
 	}
-
-	return nil
 }
 
+// sortTables sorts tables of levelHandler based on table.Smallest.
 func (s *levelHandler) sortTables() {
 	s.RLock()
 	defer s.RUnlock()

stream_writer.go

@@ -454,9 +454,11 @@ func (w *sortedWriter) createTable(builder *table.Builder) error {
 	if err := w.db.manifest.addChanges([]*pb.ManifestChange{change}); err != nil {
 		return err
 	}
-	if err := lhandler.addTables([]*table.Table{tbl}); err != nil {
-		return err
-	}
+
+	// We are not calling lhandler.replaceTables() here, as it sorts tables on every addition.
+	// We can sort all tables only once during Flush() call.
+	lhandler.addTables([]*table.Table{tbl})
+
 	// Release the ref held by OpenTable.
 	_ = tbl.DecrRef()
 	w.db.opt.Infof("Table created: %d at level: %d for stream: %d. Size: %s\n",