def garbage_collect(self, timestamp):
        stale_keys = []
        for key, window in self.occurrences.iteritems():
            if timestamp - window.data[-1][0][self.ts_field] > self.rules['timeframe']:
                stale_keys.append(key)
        map(self.occurrences.pop, stale_keys)
ensure that num_sql_queries remains consistent. Bulk create does not call
dataset/ETHPy150Open Yelp/elastalert/elastalert/ruletypes.py/FrequencyRule.garbage_collect--crossover with--dataset/ETHPy150Open django-silk/silk/silk/models.py/SQLQueryManager.bulk_create