}
//else find the score for previous receipt,
// if not exist, same as no previous receipt
// else use zrangeByScore with limit
else if (previousReceiptHandle != null) {
Double previousScore = jedis.zscore(key, previousReceiptHandle);
if (previousScore == null) {
memIds = jedis.zrangeByScore(key, System.currentTimeMillis() - retention * 1000L, System.currentTimeMillis(), 0, num);
if (memIds != null){
memIdsRet = new ArrayList<String>(memIds);
}