Can the spike system you designed pass the "Double Eleven" test?

On October 20, the annual Double Eleven kicked off. Li Jiaqi started broadcasting on time at 2:30 in the afternoon. The continuous live broadcast lasted 12 hours and 26 minutes. A total of 439 products were on the shelves, and the total transaction volume in the live broadcast room was as high as 11.5 billion yuan. , The estimated sales volume is 37.71 million. This transaction volume is close to hundreds of small-scale companies’ annual revenue. It can be seen that live e-commerce has been extremely popular in recent years, from small grass-growing bloggers to traffic stars, from Li Jiaqi, Wei Ya to Luo Yonghao, and many cities that have become rich overnight. The legend guides a massive influx of players, and all imaginable traffic with high and low levels of realisation is swarming.

As a technical practitioner of e-commerce business, high sales means high guarantee, and higher requirements for the ability of back-end engineers. Millions of users rushed into the live broadcast room, snapped up merchandise, and traffic surged. How to ensure the high availability of the system? How should the spike system be designed? What are the core challenges facing?

Technical difficulties

The spike system has: time-limited, limited, fixed-point, manual shelves, instantaneous traffic peaks, short duration and other business characteristics. Its technical characteristics are: high instantaneous concurrent flow, more reading and less writing, and simple process. Based on the above characteristics, the spike system is in Generally, the following principles should be followed when designing:

1. Asynchronous decoupling
2. Limit flow and block requests upstream as much as possible
3. Make the most of the cache

Of course, in addition to the principles that should be followed, the following issues have to be considered during the design of the spike system:

1, oversold

When the payment order quantity is greater than the current product inventory, there will be an oversold problem. For example, there are only 300 products in the inventory, but 350 units are sold in a flash sale. The oversold problem will first cause the merchant to have no goods to send, which is easy It causes complaints from merchants and users, and may cause compensation. If the coupons are oversold, it will directly cause asset loss. Therefore, the oversold problem is the primary solution when designing the spike system.

2. High concurrency

Based on the characteristics of the above spike system: short time and instantaneous traffic peaks, spikes often last only a few minutes. In high concurrency scenarios, the user's request can be simply summarized as: get cache-query data-rebuild cache-return result, if it hits the cache The result is returned directly, but a large number of concurrent requests in a short period of time may cause cache breakdown or invalidation. How to solve these problems has to be considered.

Solution

Taking the usual trading platform architecture design as an example, we need to pay attention to the establishment of trading services, scenarios, and basic capabilities. We divide the spike architecture, roughly divided into four layers: user layer, load balancing layer, application layer and persistence layer

Oversold Solution

The basic idea to solve the oversold problem is:

1. Directly rely on the DB transaction mechanism to strengthen consistency and oversold verification;
2. Ensure sufficient performance; (Ensure that the service capabilities of the DB are provided to the writing scene as much as possible)
3. Handle exceptions reasonably;
4. Deal with oversold in real time; close orders over time + increase overtime time for deducting inventory; real-time monitoring + real-time intervention
5. Try not to use asynchronous deduction of inventory

Solution: Synchronization, order to reduce inventory, code epitome:

Deduction of inventory:

UPDATE t_seckill_goods SET count = count -1, version = version +1 WHERE id = ? AND count > 0 AND version = ?

Roll back inventory:

UPDATE t_seckill_goods SET count  = count +1, version = version +1 WHERE id = ? version = ?

Of course, solving the above problems is not only a synchronous method of placing orders and reducing inventory, but also asynchronous. Returning to the spike system itself, the technical layer only solves the functional problem. For the spike in the live broadcast room, its essence is still marketing, and the essence of marketing is that attraction is not forced~

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