Improve comments

Author: ardatan

lib/query-plan-executor/src/lib.rs

@@ -519,8 +519,12 @@ impl ExecutablePlanNode for ParallelNode {
                             }
                         }
                         // We collect indexes in paths (replacing "@") to mutate the final result later
-                        // This is not a case for SequenceNode only for ParallelNode
-                        // Because in ParallelNode, we can't hold the mutable references
+                        // It might look similar to `FlattenNode.execute` which is called within `SequenceNode`
+                        // But it is not because in `SequenceNode`, we collect mutable references and mutate them during sequence execution.
+                        // While here, we collect the indexes in paths to get the mutable reference after the execution.
+                        // Collecting mutable references during traversal is possible in sequential execution which is more optimal than the following,
+                        // but in parallel execution, we need to collect indexes in paths to mutate the final result later.
+                        // We don't apply the following logic to the sequential execution, because the one there is more optimal.
                         let mut indexes_in_paths: Vec<VecDeque<usize>> = vec![];
                         traverse_and_callback(
                             data,