diff --git a/apt-sync.py b/apt-sync.py
index 1eb9dcd..71fd10b 100755
--- a/apt-sync.py
+++ b/apt-sync.py
@@ -34,6 +34,8 @@
 DOWNLOAD_TIMEOUT=int(os.getenv('DOWNLOAD_TIMEOUT', '1800'))
 REPO_SIZE_FILE = os.getenv('REPO_SIZE_FILE', '')
 
+package_info = {}
+
 pattern_os_template = re.compile(r"@\{(.+)\}")
 pattern_package_name = re.compile(r"^Filename: (.+)$", re.MULTILINE)
 pattern_package_size = re.compile(r"^Size: (\d+)$", re.MULTILINE)
@@ -98,6 +100,38 @@ def mkdir_with_dot_tmp(folder: Path)->Tuple[Path, Path]:
         shutil.rmtree(str(tmpdir))
     tmpdir.mkdir(parents=True, exist_ok=True)
     return (folder, tmpdir)
+    
+def flush_package_info(content: str):
+    
+    global package_info
+    
+    for pkg in content.split('\n\n'):
+        if len(pkg) < 10: # ignore blanks
+            continue
+        try:
+            pkg_filename = pattern_package_name.search(pkg).group(1)
+            pkg_size = int(pattern_package_size.search(pkg).group(1))
+            pkg_checksum = pattern_package_sha256.search(pkg).group(1)
+            if pkg_filename not in package_info:
+                pkg_info = {
+                    'size': pkg_size,
+                    'sha256': {
+                        'new': pkg_checksum,
+                        'old': None
+                    }
+                }
+            else:
+                pkg_info = package_info[pkg_filename]
+                pkg_info['size'] = pkg_size
+                if pkg_info['sha256']['new'] is not None and pkg_info['sha256']['old'] is None:
+                    pkg_info['sha256']['old'] = pkg_checksum
+            package_info.update({
+                pkg_filename: pkg_info
+            })
+        except:
+            print("Failed to parse one package description", flush=True)
+            traceback.print_exc()
+            return 1
 
 def move_files_in(src: Path, dst: Path):
     empty = True
@@ -110,6 +144,9 @@ def move_files_in(src: Path, dst: Path):
         print(f"{src} is empty")
 
 def apt_mirror(base_url: str, dist: str, repo: str, arch: str, dest_base_dir: Path, deb_set: Dict[str, int])->int:
+    
+    global package_info
+    
     if not dest_base_dir.is_dir():
         print("Destination directory is empty, cannot continue")
         return 1
@@ -134,6 +171,7 @@ def apt_mirror(base_url: str, dist: str, repo: str, arch: str, dest_base_dir: Pa
     pkgidx_dir,pkgidx_tmp_dir = mkdir_with_dot_tmp(comp_dir / arch_dir)
     with open(release_file, "r") as fd:
         pkgidx_content=None
+        pkgidx_file_old = None
         cnt_start=False
         for line in fd:
             if cnt_start:
@@ -146,6 +184,8 @@ def apt_mirror(base_url: str, dist: str, repo: str, arch: str, dest_base_dir: Pa
                    filename.startswith(f"Contents-{arch}"):
                     fn = Path(filename)
                     pkgidx_file = dist_dir / fn.parent / ".tmp" / fn.name
+                    if pkgidx_file.stem == 'Packages' and pkgidx_file.suffix == '':
+                        pkgidx_file_old = Path(f'{dist_dir}/{filename}')
                 else:
                     print(f"Ignore the file {filename}")
                     continue
@@ -176,12 +216,25 @@ def apt_mirror(base_url: str, dist: str, repo: str, arch: str, dest_base_dir: Pa
                         pkgidx_content = content.decode('utf-8')
                     else:
                         print("unsupported format")
+                        continue
+                    
+                    flush_package_info(pkgidx_content)
+                
+                with pkgidx_file_old.open('rb') as t: content = t.read()
+                if pkgidx_file_old.stem == 'Packages':
+                    print(f"getting packages index content from s {pkgidx_file_old.name}", flush=True)
+                    pkgidx_content_old = content.decode('utf-8')
+                    print(pkgidx_content_old)
+                    
+                    flush_package_info(pkgidx_content_old)
+                    
 
             # Currently only support SHA-256 checksum, because
             # "Clients may not use the MD5Sum and SHA1 fields for security purposes, and must require a SHA256 or a SHA512 field."
             # from https://wiki.debian.org/DebianRepository/Format#A.22Release.22_files
             if line.startswith('SHA256:'):
                 cnt_start = True
+    
     if not cnt_start:
         print("Cannot find SHA-256 checksum")
         return 1
@@ -216,18 +269,9 @@ def collect_tmp_dir():
     err = 0
     deb_count = 0
     deb_size = 0
-    for pkg in pkgidx_content.split('\n\n'):
-        if len(pkg) < 10: # ignore blanks
-            continue
-        try:
-            pkg_filename = pattern_package_name.search(pkg).group(1)
-            pkg_size = int(pattern_package_size.search(pkg).group(1))
-            pkg_checksum = pattern_package_sha256.search(pkg).group(1)
-        except:
-            print("Failed to parse one package description", flush=True)
-            traceback.print_exc()
-            err = 1
-            continue
+    for pkg_filename, pkg_info in package_info.items():
+        pkg_size = pkg_info['size']
+        pkg_checksum = pkg_info['sha256']
         deb_count += 1
         deb_size += pkg_size
 
@@ -237,8 +281,8 @@ def collect_tmp_dir():
             dest_dir.mkdir(parents=True, exist_ok=True)
         if dest_filename.suffix == '.deb':
             deb_set[str(dest_filename.relative_to(dest_base_dir))] = pkg_size
-        if dest_filename.is_file() and dest_filename.stat().st_size == pkg_size:
-            print(f"Skipping {pkg_filename}, size {pkg_size}")
+        if dest_filename.is_file() and ( dest_filename.stat().st_size == pkg_size and pkg_checksum['old'] == pkg_checksum['new']):
+            print(f"Skipping {pkg_filename}, size {pkg_size}, sha256 {pkg_checksum['new']}")
             continue
 
         pkg_url=f"{base_url}/{pkg_filename}"
@@ -253,8 +297,8 @@ def collect_tmp_dir():
             with dest_tmp_filename.open("rb") as f:
                 for block in iter(lambda: f.read(1024**2), b""):
                     sha.update(block)
-            if sha.hexdigest() != pkg_checksum:
-                print(f"Invalid checksum of {dest_filename}, expected {pkg_checksum}")
+            if sha.hexdigest() != pkg_checksum['new']:
+                print(f"Invalid checksum of {dest_filename}, expected {pkg_checksum['new']}")
                 dest_tmp_filename.unlink()
                 continue
             dest_tmp_filename.rename(dest_filename)