diff --git a/python/dgl/graphbolt/impl/ondisk_dataset.py b/python/dgl/graphbolt/impl/ondisk_dataset.py
index 64123433123b..9354974ec303 100644
--- a/python/dgl/graphbolt/impl/ondisk_dataset.py
+++ b/python/dgl/graphbolt/impl/ondisk_dataset.py
@@ -5,10 +5,12 @@
 import os
 import shutil
 import textwrap
+import time
 from copy import deepcopy
 from typing import Dict, List, Union
 
 import numpy as np
+import pandas as pd
 
 import torch
 import yaml
@@ -83,19 +85,237 @@ def _graph_data_to_fused_csc_sampling_graph(
         and "type" not in graph_data["nodes"][0]
         and "type" not in graph_data["edges"][0]
     )
-
     if is_homogeneous:
         # Homogeneous graph.
+        print("!homogeneous graph")
+        time1 = time.time()
         edge_fmt = graph_data["edges"][0]["format"]
         edge_path = graph_data["edges"][0]["path"]
         src, dst = read_edges(dataset_dir, edge_fmt, edge_path)
         num_nodes = graph_data["nodes"][0]["num"]
         num_edges = len(src)
+        ##################################################
+        # This part can we directly convert coo to csc
+        # We just have src & dst, we do not have data
+        # So for csc we just have indice & indptr
+        # we need to sort coo by its column (probably the dst)
+        # 1. Here we need the format of coo_tensor, a sample format
+        # 2. Find a proper sort function
+        # 3. consider something like bucket sort
+        # src = [0,0,1,4,4,4,6]
+        # dst = [0,2,2,2,3,4,3]
+        # num_nodes = 7
         coo_tensor = torch.tensor(np.array([src, dst]))
+        # print("coo_tensor: ", coo_tensor)
         sparse_matrix = spmatrix(coo_tensor, shape=(num_nodes, num_nodes))
         del coo_tensor
         indptr, indices, edge_ids = sparse_matrix.csc()
         del sparse_matrix
+        time2 = time.time()
+        print("total time: ", time2 - time1)
+        # A sequential version of the algorithm
+        indptr_re = [0]
+        indice_re = []
+        edge_ids_re = []
+        # In outer sort mode
+        # 1. first read in part of the csv and sort it
+        # 2. store the ordered result in the format (dst, src, original_idx) in temp csv
+        # 3. we need to add an additional label for the original edge
+        def sort_and_save_chunk(df, chunk_id, temp_dir):
+            # sort the value in every csv
+            df_sorted = df.sort_values(by=df.columns[1])
+            # columns = df_sorted.columns.tolist()
+            # 交换第一列和第二列的位置
+            # columns[0], columns[1] = columns[1], columns[0]
+            # 使用新的列顺序重新排列DataFrame
+            # df_sorted = df_sorted[columns]
+            # save the sorted csv
+            sorted_chunk_path = os.path.join(
+                temp_dir, f'sorted_chunk_{chunk_id}.npy'
+            )
+            np_array = df_sorted.to_numpy()
+            # print("np_array: ", np_array)
+            np.save(sorted_chunk_path, np_array)
+            return sorted_chunk_path
+
+        temp_dir = "temp_chunks"
+        os.makedirs(temp_dir, exist_ok=True)
+        chunk_id = 0
+        paths = []
+        # The unit for chunk_size is row number
+        chunk_size = 1000 * 1000 * 20
+        csv_path = "datasets/ogbn-products/edges/bi_edge.csv"
+        # t1 = time.time()
+        # pd.read_csv(csv_path, names=["src", "dst"])
+        # t2 = time.time()
+        # print("time for reading csv", t2-t1)
+        time2 = time.time()
+        # maybe can use some multi thread trick here, but when we use multi thread, do we reduce the memory consumption?
+        for chunk in pd.read_csv(csv_path, chunksize=chunk_size, names=["src", "dst"]):
+            t1 = time.time()
+            sorted_chunk_path = sort_and_save_chunk(chunk, chunk_id, temp_dir)
+            t2 = time.time()
+            print("time for sort_and_save_chunk: ", t2-t1)
+            paths.append(sorted_chunk_path)
+            chunk_id += 1
+        time3 = time.time()
+        print("after split: ", time3 - time2)
+        # currently this part is accelerated
+        ##################################################
+        # 3. merge the result in the temp csv
+        # 3.1 read the result in temp csv with index
+        # total_row = 0
+        # for path in paths:
+        #     sorted_chunk = pd.read_csv(path, names=["edge_id", "src", "dst"])
+        #     total_row += len(sorted_chunk)
+
+        # 4. the final result is the csv we need
+        # 4.1 here is a lemma: if we read n lines from each chunk
+        #     we can ensure that the top n element in the merged list is the smallest n
+        #     elements in the final result.
+        import heapq
+        # define the size of sorted result chunk size
+        result_chunk_size = 10000 * 1000
+
+        # a list for storing current result in memory
+        current_result_chunk = []
+        arrays_iters = []
+        heap = []
+        np_array = []
+        total_sz = 0
+        # the file path for storing the result merge file
+        output_dir_path = temp_dir + "/"
+
+        # 现在在归并排序过程中添加逻辑，以写入结果
+        for file_idx, file_path in enumerate(paths):
+            # 使用内存映射方式打开.npy file
+            # arr = np.lib.format.open_memmap(file_path, mode='r')
+            # 这里我们按照文件大小创建迭代器，每次返回一小部分数组
+            # array_iter = iter(np.array_split(arr, np.arange(chunk_size, arr.shape[0], chunk_size)))
+            # array_iter = iter(arr)
+            # array_iter = iter(np.load(file_path))
+            # arrays_iters.append(array_iter)
+            temp = np.load(file_path)
+            np_array.append(temp)
+            total_sz += temp.shape[0]
+        # merged = heapq.merge(*arrays_iters, key=lambda x: x[-1])
+        pq = []
+        pointer = []
+        xx = []
+        # print(np_array)
+        for i in range(len(np_array)):
+            pointer.append(1)
+            # numpy cannot directly push into pq, will case comparison error
+            heapq.heappush(pq, (np_array[i][0][1], np_array[i][0].tolist(), i))
+        cnt = 0
+        chunk_idx = 0
+        while(cnt < total_sz):
+            _, next_item, idx = heapq.heappop(pq)
+            current_result_chunk.append(next_item)
+            cnt += 1
+            if pointer[idx] < np_array[idx].shape[0]:
+                heapq.heappush(pq, (np_array[idx][pointer[idx]][1], np_array[idx][pointer[idx]].tolist(), idx))
+
+                pointer[idx] += 1
+            if len(current_result_chunk) == result_chunk_size:
+                with open(output_dir_path + str(chunk_idx) + "sorted.npy", 'wb') as f:
+                    np.save(f, np.array(current_result_chunk))
+                    chunk_idx += 1
+                current_result_chunk = [] 
+        # for row in merged:
+        #     current_result_chunk.append(row)
+            
+        #     # 检查当前结果块是否达到指定大小
+        #     if len(current_result_chunk) == result_chunk_size:
+        #         # 将当前结果块写入文件
+        #         with open(output_file_path, 'ab') as f:
+        #             np.save(f, np.array(current_result_chunk))
+        #         # 清空当前结果块，以便于存储新的结果
+        #         current_result_chunk = []
+
+        #     # 尝试从相同文件的迭代器中获取下一个元素
+        #     try:
+        #         next_item = next(arrays_iters[file_idx])
+        #     except StopIteration:
+        #         continue
+
+        # make sure the rest of the result is also stored in a .npy file
+        if current_result_chunk:
+            with open(output_dir_path + str(chunk_idx) + "sorted.npy", 'wb') as f:
+                np.save(f, np.array(current_result_chunk))
+                chunk_idx += 1
+        print("cnt: ", cnt)
+        print("chunk_idx", chunk_idx)
+        # data = np.load(output_file_path)
+        # print(data, data.shape)
+        print("merge finish!")
+        # 5. now we change the format of coo to a csc changeable one
+        #    Then we perform the loop before to construct a csc graph
+        last_col = -1
+        i = 0
+        time4 = time.time()
+        print("before convert to csc: ", time4 - time2)
+
+        # read in every npy file
+        for i in range(chunk_idx):
+            chunk = np.load(output_dir_path + str(i) + "sorted.npy")
+            print("chunk: ", chunk)
+            # lopp over every row in the npy file 
+            for xx in chunk:
+                # deal with every line
+                # here we need to consider the edge id, which we do not consider currently
+                # edge_id = xx[0]
+                row = xx[0]
+                col = xx[1]
+                if i >= 1 and col > last_col:
+                    for j in range(last_col + 1, col + 1):
+                        indptr_re.append(i)
+                indice_re.append(row)
+                # edge_ids_re.append(edge_id)
+                i += 1
+                last_col = col
+        # 6. remove the temp file
+        for path in paths:
+            os.remove(path)
+            # os.rmdir(temp_dir)
+        return 
+        # src_npy = np.array(src)
+        # dst_npy = np.array(dst)
+        # new_indices = np.argsort(dst_npy)
+        # sorted_src = src_npy[new_indices]
+        # sorted_dst = dst_npy[new_indices]
+        # for i in range(len(sorted_dst)):
+        #     if i >= 1 and sorted_dst[i] > sorted_dst[i-1]:
+        #         for j in range(sorted_dst[i-1] + 1, sorted_dst[i] + 1):
+        #             indptr_re.append(i)
+        #     indice_re.append(sorted_src[i])
+        #     edge_ids_re.append(new_indices[i])
+        # the upper bound
+        while (len(indptr_re) <= num_nodes):
+            indptr_re.append(len(dst))
+        
+        indptr_re = torch.tensor(indptr_re)
+        indice_re = torch.tensor(indice_re)
+        edge_ids_re = torch.tensor(edge_ids_re)
+        time5 = time.time()
+        print("total time 2: ", time5 - time2)
+        print("indptr: ", indptr, indptr.size())
+        print("indptr_re: ", indptr_re, indptr_re.size())
+        print("indices: ", indices, indices.size())
+        print("indice_re: ", indice_re, indice_re.size())
+        print("edge id: ", edge_ids)
+        print("edge_ids_re", edge_ids_re)
+       
+        # 6.0 verification
+        # a = []
+        # b = []
+        # for i in range(174):
+        #     a.append([indices[i], edge_ids[i]])
+        #     b.append([indice_re[i], edge_ids_re[i]])
+        # a.sort()
+        # b.sort()
+        # print("a:", a[:10])
+        # print("b:", b[:10])
 
         if auto_cast_to_optimal_dtype:
             if num_nodes <= torch.iinfo(torch.int32).max: