Traceback (most recent call last):
  File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/seed/seeder.py", line 122, in run
    self.work_loop()
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/seed/seeder.py", line 134, in work_loop
    exceptions=(SourceError, IOError), ignore_exceptions=(LockTimeout, ))
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/seed/util.py", line 222, in exp_backoff
    result = func(*args, **kw)
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/tile.py", line 127, in load_tile_coords
    created_tiles = creator.create_tiles(uncached_tiles)
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/tile.py", line 229, in create_tiles
    created_tiles = self._create_meta_tiles(meta_tiles)
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/tile.py", line 302, in _create_meta_tiles
    created_tiles.extend(self._create_meta_tile(meta_tile))
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/tile.py", line 318, in _create_meta_tile
    self.cache.store_tiles(splitted_tiles)
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/base.py", line 61, in store_tiles
    if not self.store_tile(tile):
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/mbtiles.py", line 295, in store_tile
    return self._get_level(tile.coord[2]).store_tile(tile)
  File "/opt/mapproxy/lib/python2.7/site-packages/mapproxy/cache/mbtiles.py", line 149, in store_tile
    cursor.execute(stmt, (level, x, y, content, time.time()))
OperationalError: database is locked