@classmethod
  def ScanAbandoned(cls, client, callback, limit=None, excl_start_key=None):
    assert limit > 0, limit
    now = int(time.time())
    Lock.Scan(client, None, callback, limit=limit,
              excl_start_key=excl_start_key,
              scan_filter={'expiration': db_client.ScanFilter([now], 'LE')})
Scans the Lock table for locks that have expired, and therefore
dataset/ETHPy150Open viewfinderco/viewfinder/backend/db/lock.py/Lock.ScanAbandoned