Improve performance for creating crdt.TreeNode (#939)

The time complexity of creating crdt.TreeNode is O(N^2), potentially
causing performance bottlenecks. It's optimized to O(n).

While this may not be a significant issue currently, there is a risk
that as the number of tree nodes in the protobuf increases, operations
will scale quadratically, potentially causing performance bottlenecks.

---------

Co-authored-by: JiHwan Yim <[email protected]>
Co-authored-by: Youngteac Hong <[email protected]>

api/converter/from_pb.go

@@ -583,18 +583,15 @@ func FromTreeNodes(pbNodes []*api.TreeNode) (*crdt.TreeNode, error) {
 	}
 
 	root := nodes[len(nodes)-1]
+	depthTable := make(map[int32]*crdt.TreeNode)
+	depthTable[pbNodes[len(nodes)-1].Depth] = nodes[len(nodes)-1]
 	for i := len(nodes) - 2; i >= 0; i-- {
-		var parent *crdt.TreeNode
-		for j := i + 1; j < len(nodes); j++ {
-			if pbNodes[i].Depth-1 == pbNodes[j].Depth {
-				parent = nodes[j]
-				break
-			}
-		}
+		var parent *crdt.TreeNode = depthTable[pbNodes[i].Depth-1]
 
 		if err := parent.Prepend(nodes[i]); err != nil {
 			return nil, err
 		}
+		depthTable[pbNodes[i].Depth] = nodes[i]
 	}
 
 	root.Index.UpdateDescendantsSize()

test/bench/tree_editing_bench_test.go

@@ -0,0 +1,67 @@
+//go:build bench
+
+/*
+ * Copyright 2024 The Yorkie Authors. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package bench
+
+import (
+	"testing"
+
+	"github.com/yorkie-team/yorkie/api/converter"
+	api "github.com/yorkie-team/yorkie/api/yorkie/v1"
+	"github.com/yorkie-team/yorkie/pkg/document/json"
+	"github.com/yorkie-team/yorkie/test/helper"
+)
+
+// bench mark converting from protobuf tree nodes to crdt.TreeNode
+func BenchmarkTreeConverting(b *testing.B) {
+	b.Run("1000 vertex tree converting test", func(b *testing.B) {
+		TreeConverting(1000, b)
+	})
+
+	b.Run("10000 vertex tree converting test", func(b *testing.B) {
+		TreeConverting(10000, b)
+	})
+
+	b.Run("100000 vertex tree converting test", func(b *testing.B) {
+		TreeConverting(100000, b)
+	})
+}
+
+// MakeTree is a helper function to create simple tree.
+func MakeTree(vertexCnt int) []*api.TreeNode {
+	var chd []json.TreeNode
+	for i := 0; i < vertexCnt; i++ {
+		chd = append(chd, json.TreeNode{Type: "p", Children: []json.TreeNode{{Type: "text", Value: "a"}}})
+	}
+
+	root := helper.BuildTreeNode(&json.TreeNode{
+		Type:     "r",
+		Children: chd,
+	})
+
+	pbNodes := converter.ToTreeNodes(root)
+	return pbNodes
+}
+
+func TreeConverting(vertexCnt int, b *testing.B) {
+	b.StopTimer()
+	pbNodes := MakeTree(vertexCnt)
+	b.StartTimer()
+
+	converter.FromTreeNodes(pbNodes)
+}