diff --git a/database.py b/database.py
index 09908d1..a51bb7e 100644
--- a/database.py
+++ b/database.py
@@ -26,17 +26,6 @@ def db_execute(*args, **kwargs):
 		DB_LOCK.release()
 		return res
 
-def db_execute_unsafe(*args, **kwargs):
-	"""
-	A non-thread-safe version of `db_execute()`. Only use if you're
-	certain there will be no competing threads for the database.
-	"""
-	with sqlite3.connect('musik.db') as con:
-		con.row_factory = sqlite3.Row
-		cur = con.cursor()
-		res = cur.execute(*args, **kwargs)
-		return res
-
 def db_execute_many(*args, **kwargs):
 	"""
 	Same as `db_executei()` except with `cur.executemany()`.
@@ -54,8 +43,9 @@ def init_database():
 	Initializes the database.
 	"""
 	try:
-		db_execute_unsafe("SELECT * FROM tracks LIMIT 1").fetchone()
+		db_execute("SELECT * FROM tracks LIMIT 1").fetchone()
 	except sqlite3.OperationalError:
+		DB_LOCK.release()
 		db_execute("CREATE TABLE tracks("
 			"filepath TEXT PRIMARY KEY,"
 			"artist TEXT,"
@@ -66,7 +56,8 @@ def init_database():
 			"tracknumber TEXT,"
 			"title TEXT,"
 			"genre TEXT,"
-			"length TEXT"
+			"length TEXT,"
+			"last_modified INTEGER"
 			")"
 		)
 		build_library(MUSIC_DIR)
@@ -81,11 +72,19 @@ def build_library(root_dir):
 			if not os.path.splitext(file)[1][1:] in MUSIC_EXT:
 				continue
 			filepath = os.path.join(root_dir, dir_name, file)
-			filepaths.append(filepath)
+			last_modified = os.path.getmtime(filepath)
+			filepaths.append((filepath, last_modified))
+	tracks_prev = db_execute("SELECT * FROM tracks")
+	tracks_prev = {track['filepath']: track for track in tracks_prev}
 
 	global worker
-	def worker(filepath):
+	def worker(tup):
 		"""Worker for multi-processing tracks."""
+		filepath, last_modified = tup
+		track_prev = tracks_prev.get(filepath)
+		if track_prev:
+			if track_prev['last_modified'] >= last_modified:
+				return tuple(track_prev)
 		data = read_track(filepath)
 		return data
 
@@ -102,8 +101,9 @@ def build_library(root_dir):
 			if percent >= prev_percent + 2.5:
 				print(f"{percent}%")
 				prev_percent = percent
+	db_execute("DELETE FROM tracks")
 	db_execute_many(
-		"INSERT INTO tracks VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
+		"INSERT INTO tracks VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
 		tracks
 	)
 	print("Done")
@@ -131,23 +131,13 @@ def read_track(filepath):
 	genre = m.get('genre', [''])[0]
 	length = str(int(m.info.length) // 60) + ":"
 	length += str(int(m.info.length) % 60)
+	last_modified = os.path.getmtime(filepath)
 
 	d = locals()
 	d.pop('m')
 	return tuple(d.values())
 
 
-def insert_track(data):
-	"""
-	Inserts a new item into the `tracks` table. `data` should be a tuple
-	containing an item for every column in the `tracks` table. See the
-	table declarion in `init_database()` for more information.
-	"""
-	db_execute(
-		"INSERT INTO tracks VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)",
-		data
-	)
-
 def get_artist_albums(artist):
 	"""
 	Returns a list of all albums produced by the specified `artist`.
diff --git a/musik.py b/musik.py
index 6b23047..6ce7324 100755
--- a/musik.py
+++ b/musik.py
@@ -116,4 +116,7 @@ def coverart():
 
 
 if __name__ == "__main__":
+	import sys
+	if len(sys.argv) > 1:
+		database.build_library(database.MUSIC_DIR)
 	app.run(host='0.0.0.0', port=5150)