mysql + nest.js  加锁搞并发问题的实现

CREATE TABLE goods (
  id INT PRIMARY KEY AUTO_INCREMENT,
  name VARCHAR(100),
  stock INT NOT NULL,
  price DECIMAL(10,2),
  create_time DATETIME DEFAULT CURRENT_TIMESTAMP
);

CREATE TABLE orders (
  id INT PRIMARY KEY AUTO_INCREMENT,
  user_id INT,
  goods_id INT,
  create_time DATETIME DEFAULT CURRENT_TIMESTAMP
);

INSERT INTO goods (name, stock, price)
VALUES ('iphone 15', 10, 8999);

const goods = await db.query('SELECT * FROM goods WHERE id = ?', [id])

if (goods.stock > 0) {
  await db.query('UPDATE goods SET stock = stock - 1 WHERE id = ?', [id])
}

UPDATE goods
SET stock = stock - 1
WHERE id = ? AND stock > 0;

npm install mysql2

import { Injectable } from '@nestjs/common'
import * as mysql from 'mysql2/promise'

@Injectable()
export class MysqlService {

  pool = mysql.createPool({
    host: 'localhost',
    user: 'root',
    password: '123456',
    database: 'test',
    connectionLimit: 10
  })

  async query(sql: string, params?: any[]) {
    const [rows] = await this.pool.execute(sql, params)
    return rows
  }

}

import { Injectable } from '@nestjs/common'
import { MysqlService } from './mysql.service'

@Injectable()
export class SeckillService {

  constructor(private db: MysqlService) {}

  async buy(userId: number, goodsId: number) {

    // 1 扣库存（原子SQL）
    const result: any = await this.db.query(
      `UPDATE goods 
       SET stock = stock - 1 
       WHERE id = ? AND stock > 0`,
      [goodsId]
    )

    if (result.affectedRows === 0) {
      return {
        message: '库存不足'
      }
    }

    // 2 创建订单
    await this.db.query(
      `INSERT INTO orders (user_id, goods_id) VALUES (?, ?)`,
      [userId, goodsId]
    )

    return {
      message: '秒杀成功'
    }

  }

}

import { Controller, Post, Body } from '@nestjs/common'
import { SeckillService } from './seckill.service'

@Controller('seckill')
export class SeckillController {

  constructor(private seckillService: SeckillService) {}

  @Post('buy')
  async buy(@Body() body) {

    const { userId, goodsId } = body

    return this.seckillService.buy(userId, goodsId)

  }

}

UPDATE goods SET stock = stock - 1 WHERE id=1 AND stock>0

stock = -1

Redis      防止打爆数据库
MQ         削峰
MySQL      最终一致

SELECT * FROM goods WHERE id = 1 FOR UPDATE;

const conn = await this.db.pool.getConnection()

try {

  await conn.beginTransaction()

  const [goods]: any = await conn.query(
    'SELECT * FROM goods WHERE id = ? FOR UPDATE',
    [goodsId]
  )

  if (goods.length === 0 || goods[0].stock <= 0) {
    await conn.rollback()
    return { message: '库存不足' }
  }

  await conn.query(
    'UPDATE goods SET stock = stock - 1 WHERE id = ?',
    [goodsId]
  )

  await conn.query(
    'INSERT INTO orders (user_id, goods_id) VALUES (?, ?)',
    [userId, goodsId]
  )

  await conn.commit()

  return { message: '购买成功' }

} catch (err) {

  await conn.rollback()
  throw err

} finally {

  conn.release()

}

UPDATE goods 
SET stock = stock - 1 
WHERE id = 1 AND stock > 0
LIMIT 1;