Using Redis in PHP to implement flash sale activities

With the development of the e-commerce industry, flash sale activities have become one of the important ways for major platforms to attract users. As the number of users increased, the original server could not withstand the instantaneous traffic, causing the server to crash and unable to continue flash sale activities. In order to solve this problem, we can use Redis to implement flash sales activities.

Redis is a memory-based high-performance NoSQL database. Its main purpose is to cache and reduce the pressure on the database. In the flash sale activity, Redis has the following advantages:

1. High-speed reading and writing: Redis is based on memory, has very fast reading and writing speeds, and can handle high-concurrency requests.
2. High reliability: Redis supports master-slave replication and data persistence, which can realize data backup and recovery and ensure data reliability and consistency.
3. High concurrency: Redis adopts a single-threaded model, which avoids the problems of thread switching and lock competition, and can handle a large number of concurrent requests.

Next, we will introduce in detail how to use Redis to implement flash sale activities.

1. Product inventory management

First, we need to set the inventory information of the product in Redis. In the flash sale activity, the inventory of the product is very important, which determines the order quantity that the flash sale activity can accept. We can use the hash type of Redis to store the inventory information of the product, where the key is the id of the product and the value is the inventory quantity of the product.

For example, we can use the following command to set the inventory of the product with id 1 to 100:

> HSET goods:1 stock 100

2. Flash sale order processing

In the flash sale activity , users can submit orders to purchase flash sale products. However, due to the very large number of visits to the flash sale activity, it may cause the server to crash or the response time to be too long. To solve this problem, we can use Redis queue to process orders.

First, we need to create two queues: order queue and inventory queue. The order queue is used to store orders submitted by users, and the inventory queue is used to store remaining inventory. When the user submits an order, we store the order information in the order queue and reduce the inventory quantity in the inventory queue by 1, indicating that someone has already snapped up the product.

For example, we can use the following commands to create order queues and inventory queues:

> LPUSH orders goods:1:userId
> LPUSH stocks goods:1

where orders is the order queue, and the LPUSH command adds the order information goods:1:userId to the head of the queue . userId is the user's id.

stocks is the inventory queue, and the LPUSH command adds the product id goods:1 to the head of the queue.

In the order queue, we use the combination of product ID and user ID as the unique identifier of the order to avoid repeated submission of orders.

3. Flash Sale Activity Processing

Before the flash sale activity starts, we need to limit each user to only one purchase to prevent users from maliciously submitting orders. We can use Redis's set type to store the user ID that has been purchased.

For example, we can use the following command to add the id of the purchased user:

> SADD users:goods1 userId

During the flash sale activity, we can use Lua scripts to handle inventory deductions and order generation. Lua scripts can ensure the atomicity of inventory and order processing, avoiding inventory errors and order duplication caused by concurrent requests.

For example, the following is a piece of code that uses Lua script to process the flash sale activity:

local userId = ARGV[1]
local goodsId = ARGV[2]

-- 判断用户是否已经购买过该商品
if redis.call("SISMEMBER", "users:" .. goodsId, userId) == 1 then
   return 0
end

-- 判断库存是否为空
if redis.call("LLEN", "stocks:" .. goodsId) == 0 then
   return -1
end

-- 将用户id加入已购买用户的集合
redis.call("SADD","users:" .. goodsId, userId)

-- 从库存队列中弹出商品id
local stockGoods = redis.call("RPOP", "stocks:" .. goodsId)
-- 在订单队列中添加订单
redis.call("LPUSH", "orders", goodsId .. ":" .. userId)

-- 返回商品id
return stockGoods

4. End of flash sale activity

After the flash sale activity ends, we The remaining inventory needs to be restored for the next event. We can use the following command to restore inventory:

> HINCRBY goods:1 stock 50
> LPUSH stocks goods:1

Add the remaining inventory quantity to the inventory information of the item, and then add the item id to the tail of the inventory queue.

To sum up, we can use Redis to implement flash sales activities, while avoiding problems such as server pressure and users maliciously submitting orders, making the flash sales activities smoother and fairer.

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