diff --git a/generate_data.py b/generate_data.py
index fd5924e..0f12e05 100644
--- a/generate_data.py
+++ b/generate_data.py
@@ -105,34 +105,37 @@ def calculate_distance(pair):
     distance = get_distance(city1["name"], city2["name"])
     return city1["name"], city2["name"], distance
 
-
 def main():
     cities = list(us_cities.values())
     print(f"Num cities: {len(cities)}")
     city_combinations = list(itertools.combinations(cities, 2))
+    chunk_size = 800  # adjust this as needed
+    num_chunks = len(city_combinations) // chunk_size + 1
+    output_file = args.output_file
 
-    with open(args.output_file, "w", newline="") as csvfile:
+    with open(output_file, "w", newline="") as csvfile:
         fieldnames = ["city_from", "city_to", "distance"]
         writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
         writer.writeheader()
 
         try:
             executor = concurrent.futures.ProcessPoolExecutor(max_workers=args.workers)
-            # results = executor.map(calculate_distance, city_combinations)
-            futures = {
-                executor.submit(calculate_distance, pair): pair
-                for pair in city_combinations
-            }
-            for future in as_completed(futures):
-                city_from, city_to, distance = future.result()
-                if distance is not None:
-                    writer.writerow(
-                        {
-                            "city_from": city_from,
-                            "city_to": city_to,
-                            "distance": distance,
-                        }
-                    )
+            for i in range(num_chunks):
+                chunk = city_combinations[i * chunk_size : (i + 1) * chunk_size]
+                futures = {
+                    executor.submit(calculate_distance, pair): pair for pair in chunk
+                }
+                for future in as_completed(futures):
+                    city_from, city_to, distance = future.result()
+                    if distance is not None:
+                        writer.writerow(
+                            {
+                                "city_from": city_from,
+                                "city_to": city_to,
+                                "distance": distance,
+                            }
+                        )
+                        csvfile.flush()  # write to disk immediately
         except KeyboardInterrupt:
             print("Interrupted. Terminating processes...")
             executor.shutdown(wait=False)