Said ahead

Management Request GET_MIN_OFFSET Gets Minimum offset

Source code analysis
Enter the method org.apache.rocketmq.broker.processor.AdminBrokerProcessor#getMinOffset to get the smallest offset

 private RemotingCommand getMinOffset(ChannelHandlerContext ctx,
        RemotingCommand request) throws RemotingCommandException {
        final RemotingCommand response = RemotingCommand.createResponseCommand(GetMinOffsetResponseHeader.class);
        final GetMinOffsetResponseHeader responseHeader = (GetMinOffsetResponseHeader) response.readCustomHeader();
        final GetMinOffsetRequestHeader requestHeader =
            (GetMinOffsetRequestHeader) request.decodeCommandCustomHeader(GetMinOffsetRequestHeader.class);
//        Find the smallest offset = based on topic and queueId
        long offset = this.brokerController.getMessageStore().getMinOffsetInQueue(requestHeader.getTopic(), requestHeader.getQueueId());
        responseHeader.setOffset(offset);
        response.setCode(ResponseCode.SUCCESS);
        response.setRemark(null);
        return response;
    }

Enter the method org.apache.rocketmq.store.DefaultMessageStore#getMinOffsetInQueue to query the smallest offset based on topic and queueId

public long getMinOffsetInQueue(String topic, int queueId) {
//        Query the consumer queue= based on topic and queueId
        ConsumeQueue logic = this.findConsumeQueue(topic, queueId);
        if (logic != null) {
//            Get the minimum offset in the queue
            return logic.getMinOffsetInQueue();
        }

        return -1;
    }

Enter the method org.apache.rocketmq.store.DefaultMessageStore#findConsumeQueue to query the consumption queue by topic and queueId, as described earlier.

public ConsumeQueue findConsumeQueue(String topic, int queueId) {
        ConcurrentMap<Integer, ConsumeQueue> map = consumeQueueTable.get(topic);
        if (null == map) {
            ConcurrentMap<Integer, ConsumeQueue> newMap = new ConcurrentHashMap<Integer, ConsumeQueue>(128);
            ConcurrentMap<Integer, ConsumeQueue> oldMap = consumeQueueTable.putIfAbsent(topic, newMap);
            if (oldMap != null) {
                map = oldMap;
            } else {
                map = newMap;
            }
        }

//        Find the consumer queue by queue id
        ConsumeQueue logic = map.get(queueId);
        if (null == logic) {
            ConsumeQueue newLogic = new ConsumeQueue(
                topic,
                queueId,
//                Consumer queue storage address user.home/store/consumequeue
                StorePathConfigHelper.getStorePathConsumeQueue(this.messageStoreConfig.getStorePathRootDir()),
//                Default 30W per file store
                this.getMessageStoreConfig().getMapedFileSizeConsumeQueue(),
                this);
            ConsumeQueue oldLogic = map.putIfAbsent(queueId, newLogic);
            if (oldLogic != null) {
                logic = oldLogic;
            } else {
                logic = newLogic;
            }
        }

        return logic;
    }

Go back up to the end of the method org.apache.rocketmq.broker.processor.AdminBrokerProcessor#getMinOffset

Said at the end

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