resort maximum_resort_levels tweak implemented

resources/default_tweaks.py

@@ -114,3 +114,10 @@
 # Set the maximum number of tags to show per book in the content server
 max_content_server_tags_shown=5
 
+
+# Set the maximum number of sort 'levels' that calibre will use to resort the
+# library after certain operations such as searches or device insertion. Each
+# sort level adds a performance penalty. If the database is large (thousands of
+# books) the penalty might be noticeable. If you are not concerned about multi-
+# level sorts, and if you are seeing a slowdown, reduce the value of this tweak.
+maximum_resort_levels = 5

src/calibre/gui2/library/models.py

@@ -266,8 +266,8 @@ def refresh(self, reset=True):
         self.db.refresh(field=None)
         self.resort(reset=reset)
 
-    def resort(self, reset=True, history=5): # Bug report needed history=4 :)
-        for col,ord in reversed(self.sort_history[:history]):
+    def resort(self, reset=True):
+        for col,ord in reversed(self.sort_history[:tweaks['maximum_resort_levels']]):
             try:
                 col = self.column_map.index(col)
             except ValueError: