btr0cur.c:

  Backport from 4.0: Fix a major bug in InnoDB query estimator for queries of type SELECT ... WHERE col < x and SELECT ... WHERE col > x; MySQL could pick a table scan though the result set was only a few rows in a big table

innobase/btr/btr0cur.c

@@ -577,11 +577,11 @@ btr_cur_open_at_index_side(
 			page_cur_set_after_last(page, page_cursor);
 		}
 
-		if (estimate) {
-			btr_cur_add_path_info(cursor, height, root_height);
-		}
-
 		if (height == 0) {
+		        if (estimate) {
+			        btr_cur_add_path_info(cursor, height,
+						      root_height);
+		        }
 
 			break;
 		}
@@ -594,6 +594,10 @@ btr_cur_open_at_index_side(
 			page_cur_move_to_prev(page_cursor);
 		}
 
+		if (estimate) {
+			btr_cur_add_path_info(cursor, height, root_height);
+		}
+
 		height--;
 
 		node_ptr = page_cur_get_rec(page_cursor);