03. 履约链路业务流程分析

订单履约状态通知乱序问题分析

1. 第一步，调度出库，仓库操作员根据订单进行拣货出库；
2. 第二步，物流配送，快递员将商品打包邮寄配送；
3. 第三步，完成签收，消费者最终完成签收；

都会产生一个订单履约状态的消息，投递到RocketMQ，订单服务专门的线程负责消费处理，更新订单状态；

分析一下订单履约状态通知乱序的问题，可能导致订单状态数据错乱；

通过将同一个订单的履约状态消息投递到同一个ConsumerQueue；

另外，思考一下，履约状态消息消费过程中，怎么保证幂等消费（分布式锁），同时，如果消费出现异常，又要怎么保证履约状态消息的顺序性（SUSPEND_CURRENT_QUEUE_A_MOMENT，消息挂起）；

SendResult sendResult = defaultMQProducer.send(message, new MessageQueueSelector() {
	@Override
	public MessageQueue select(List<MessageQueue> mqs, Message message, Object arg) {
		//根据订单id选择发送queue
		String orderId = (String) arg;
		long index = hash(orderId) % mqs.size();
		return mqs.get((int) index);
	}
}, orderId);

需要关注一下这里设计模式的一些应用实战；

思考一下，如何保证 1. 履约服务，创建履约单；2. 通知仓储服务，调度出库发货；3. 通知物流服务，物流配送；强一致性问题；

引入 Seata Saga长事务机制，缺点，没有全局锁概念，没有写隔离机制；

适用场景，业务链路比较长，耗时较长的特定业务场景；

{
    "Name": "order_fulfill",
    "Comment": "订单履约流程",
    "StartState": "FulfillService",
    "Version": "1.0.0",
    "States": {
        "FulfillService": {
            "Type": "ServiceTask",
            "ServiceName": "fulfillSagaService",
            "ServiceMethod": "createFulfillOrder",
            "CompensateState": "CreateFulfillOrderCompensate",
            "Next": "ChoiceWmsState",
            "Input": [
                "$.[receiveFulfillRequest]"
            ],
            "Output": {
                "CreateFulfillOrderResult": "$.#root"
            },
            "Status": {
                "#root == true": "SU",
                "#root == false": "FA",
                "$Exception{java.lang.Throwable}": "UN"
            },
            "Catch": [
                {
                    "Exceptions": [
                        "java.lang.Throwable"
                    ],
                    "Next": "CompensationTrigger"
                }
            ]
        },
        "ChoiceWmsState":{
            "Type": "Choice",
            "Choices":[
                {
                    "Expression":"[CreateFulfillOrderResult] == true",
                    "Next":"WmsService"
                }
            ],
            "Default":"Fail"
        },
        "WmsService": {
            "Type": "ServiceTask",
            "ServiceName": "wmsSageService",
            "ServiceMethod": "pickGoods",
            "CompensateState": "WmsPickGoodsCompensate",
            "Next": "ChoiceTmsState",
            "Input": [
                "$.[receiveFulfillRequest]"
            ],
            "Output": {
                "WmsPickGoodsResult": "$.#root"
            },
            "Status": {
                "#root == true": "SU",
                "#root == false": "FA",
                "$Exception{java.lang.Throwable}": "UN"
            },
            "Catch": [
                {
                    "Exceptions": [
                        "java.lang.Throwable"
                    ],
                    "Next": "CompensationTrigger"
                }
            ]
        },
        "ChoiceTmsState":{
            "Type": "Choice",
            "Choices":[
                {
                    "Expression":"[WmsPickGoodsResult] == true",
                    "Next":"TmsService"
                }
            ],
            "Default":"Fail"
        },
        "TmsService": {
            "Type": "ServiceTask",
            "ServiceName": "tmsSagaService",
            "ServiceMethod": "sendOut",
            "CompensateState": "TmsSendOutCompensate",
            "Input": [
                "$.[receiveFulfillRequest]"
            ],
            "Output": {
                "TmsSendOutResult": "$.#root"
            },
            "Status": {
                "#root == true": "SU",
                "#root == false": "FA",
                "$Exception{java.lang.Throwable}": "UN"
            },
            "Catch": [
                {
                    "Exceptions": [
                        "java.lang.Throwable"
                    ],
                    "Next": "CompensationTrigger"
                }
            ],
            "Next": "Succeed"
        },
        "CreateFulfillOrderCompensate": {
            "Type": "ServiceTask",
            "ServiceName": "fulfillSagaService",
            "ServiceMethod": "createFulfillOrderCompensate",
            "Input": [
                "$.[receiveFulfillRequest]"
            ]
        },
        "WmsPickGoodsCompensate": {
            "Type": "ServiceTask",
            "ServiceName": "wmsSageService",
            "ServiceMethod": "pickGoodsCompensate",
            "Input": [
                "$.[receiveFulfillRequest]"
            ]
        },
        "TmsSendOutCompensate": {
            "Type": "ServiceTask",
            "ServiceName": "tmsSagaService",
            "ServiceMethod": "sendOutCompensate",
            "Input": [
                "$.[receiveFulfillRequest]"
            ]
        },
        "CompensationTrigger": {
            "Type": "CompensationTrigger",
            "Next": "Fail"
        },
        "Succeed": {
            "Type":"Succeed"
        },
        "Fail": {
            "Type":"Fail",
            "ErrorCode": "500",
            "Message": "订单履约异常！！"
        }
    }
}

Seata Saga 长事务运行原理

思考一下，空补偿，空回滚的问题，具体方案参考之前 Seata TCC 模式处理锁定库存的代码实现；