diff --git a/bin/swh-diff-db-mirror b/bin/swh-diff-db-mirror
index ed56a88..b4a4def 100755
--- a/bin/swh-diff-db-mirror
+++ b/bin/swh-diff-db-mirror
@@ -1,120 +1,73 @@
 #!/usr/bin/env python3
 
 # Copyright (C) 2015  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import argparse
 import os
-import psycopg2
 import sys
 
-from swh.loader.tar import tarball
-
-
-def connect(db_url):
-    """Open db connection.
-    """
-    return psycopg2.connect(db_url)
-
-
-def execute(cur, query_params):
-    """Execute the query_params.
-    query_params is expected to be either:
-    - a sql query (string)
-    - a tuple (sql query, params)
-    """
-    if isinstance(query_params, str):
-        cur.execute(query_params)
-    else:
-        cur.execute(*query_params)
-
-
-def query_fetch(db_conn, query_params):
-    """Execute sql query which returns results.
-    query_params is expected to be either:
-    - a sql query (string)
-    - a tuple (sql query, params)
-    """
-    with db_conn.cursor() as cur:
-        execute(cur, query_params)
-        yield from cursor_to_bytes(cur)
-
-
-def entry_to_bytes(entry):
-    """Convert an entry coming from the database to bytes"""
-    if isinstance(entry, memoryview):
-        return entry.tobytes()
-    return entry
-
-
-def line_to_bytes(line):
-    """Convert a line coming from the database to bytes"""
-    return line.__class__(entry_to_bytes(entry) for entry in line)
-
-
-def cursor_to_bytes(cursor):
-    """Yield all the data from a cursor as bytes"""
-    yield from (line_to_bytes(line) for line in cursor)
+from swh.loader.tar import tarball, db
 
 
 def list_branches(db_url):
     """Return the distinct list of branches present in occurrence_history.
 
     """
-    with connect(db_url) as db_conn:
-        for branch in query_fetch(db_conn,
-                                  'select distinct branch from '
-                                  'occurrence_history'):
+    with db.connect(db_url) as db_conn:
+        for branch in db.query_fetch(db_conn,
+                                     'select distinct branch from '
+                                     'occurrence_history'):
             yield branch[0]
 
 
 def diff_branch(root_dir, existing_set):
     """Walk the root_dir and for every tarball not in existing_set,
     yield its absolute path.
 
     """
     for dirpath, _, filenames in os.walk(root_dir):
         for filename in filenames:
             filepath = os.path.join(dirpath, filename)
             if not os.path.exists(filepath):
                 continue
             if not tarball.is_tarball(filepath):
                 continue
             if filename in existing_set:
                 continue
 
             yield filepath
 
 
 def parse_args():
     """Parse the configuration from the cli.
 
     """
     cli = argparse.ArgumentParser(
         description='Diff between db and local fs mirror tarballs directory.'
                     'Output what\'s on disk and not on db.')
     cli.add_argument('--db-url', '-d',
                      help='db-url string')
     cli.add_argument('--mirror-root-directory', '-m',
                      help='mirror root directory')
 
     args = cli.parse_args()
     if not args.db_url or not args.mirror_root_directory:
         print('Bad usage, cf. --help')
         sys.exit(1)
 
     return args
 
 
 if __name__ == '__main__':
     args = parse_args()
 
     db_url = args.db_url
 
     already_present = set(list_branches(db_url))
 
     root_dir = args.mirror_root_directory
     for filepath in diff_branch(root_dir, already_present):
         print(filepath)
diff --git a/swh/loader/tar/db.py b/swh/loader/tar/db.py
new file mode 100644
index 0000000..961af03
--- /dev/null
+++ b/swh/loader/tar/db.py
@@ -0,0 +1,52 @@
+# Copyright (C) 2015  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+import psycopg2
+
+
+def connect(db_url):
+    """Open db connection.
+    """
+    return psycopg2.connect(db_url)
+
+
+def execute(cur, query_params):
+    """Execute the query_params.
+    query_params is expected to be either:
+    - a sql query (string)
+    - a tuple (sql query, params)
+    """
+    if isinstance(query_params, str):
+        cur.execute(query_params)
+    else:
+        cur.execute(*query_params)
+
+
+def entry_to_bytes(entry):
+    """Convert an entry coming from the database to bytes"""
+    if isinstance(entry, memoryview):
+        return entry.tobytes()
+    return entry
+
+
+def line_to_bytes(line):
+    """Convert a line coming from the database to bytes"""
+    return line.__class__(entry_to_bytes(entry) for entry in line)
+
+
+def cursor_to_bytes(cursor):
+    """Yield all the data from a cursor as bytes"""
+    yield from (line_to_bytes(line) for line in cursor)
+
+
+def query_fetch(db_conn, query_params):
+    """Execute sql query which returns results.
+    query_params is expected to be either:
+    - a sql query (string)
+    - a tuple (sql query, params)
+    """
+    with db_conn.cursor() as cur:
+        execute(cur, query_params)
+        yield from cursor_to_bytes(cur)