Redis——作为sql数据库缓存

Dear 丶 2023-10-11 11:08 9阅读 0赞

**一、环境springBoot：**

1）导入依赖：

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<dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-redis</artifactId>
            </dependency>

依赖

2）配置文件 application.yml

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spring:
      redis:
        host: 192.168.2.147
        port: 6379
        password: java1902
        jedis:
          pool:
            max-active: 100

application.yml

**二、redis作为数据库缓存：**

原理：第一次查询使用sql数据库，查询完成后把数据存入redis用于后续查询，直到sql中的数据变化，清空相应的redis缓存，重新获取；

缓存失效：更新数据库，采用清空redis缓存的方式；

1）实体类：

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public class Product implements Serializable {
        private Integer id;
        private String name;
    
        public Product() {
        }
    
        public Product(Integer id, String name) {
            this.id = id;
            this.name = name;
        }
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        @Override
        public String toString() {
            return "Product{" +
                    "id=" + id +
                    ", name='" + name + '\'' +
                    '}';
        }
    }

实体类

2）测试：

@RunWith(SpringRunner.class)
    @SpringBootTest
    public class RedistestSpringData2ApplicationTests {
        @Autowired
        private RedisTemplate redisTemplate;
    
        @Test
        public void cacheTest() {
            List<Product> products = (List<Product>) redisTemplate.opsForValue().get("product:");
            if (products == null) {
                System.out.println("查询数据库......");
                // 模拟从数据库查询数据
                products = new ArrayList<Product>();
                products.add(new Product(1, "商品1"));
                products.add(new Product(2, "商品2"));
    
                redisTemplate.opsForValue().set("product:", products);
            } else {
                System.out.println("查询缓存......");
            }
        }
    
        @Test
        public void delCacheTest() {
            redisTemplate.delete("product:");
        }
    
    }

**三、解决缓存穿透问题：**

原因：一个线程在访问数据库信息后还未写入到缓存时丢失了时间片，其它线程访问时重复访问了数据库，造成数据库巨大压力；

解决：

1）synchronized来加锁：因为是分布式开发，synchronized的作用域是JVM，则在多个服务间synchronized是无效的；

2）Redis分布式锁：

1、在redis本地使用：

setnx Lock 1 //1
    get Lock //1
    setnx Lock 2 //00
    del Lock
    setnx Locks 2 //1

2、springboot代码实现：

//try finally解决死锁问题：

@RunWith(SpringRunner.class)
    @SpringBootTest
    public class RedistestSpringData2ApplicationTests {
        @Autowired
        private RedisTemplate redisTemplate;
    
        @Test
        public void multiThreadTest() throws InterruptedException {
            ExecutorService pool = new ThreadPoolExecutor(100, 200, 100, TimeUnit.MILLISECONDS,
                    new LinkedBlockingDeque<>(100));
            for (int i = 0; i < 100; i++) {
                pool.submit(new Runnable() {
                    @Override
                    public void run() {
                        cacheTest();
                    }
                });
            }
            Thread.sleep(1000000);
        }
    
        @Test
        public void cacheTest() {
            List<Product> products = (List<Product>) redisTemplate.opsForValue().get("product:");
            if (products == null) {
                Boolean ifAbsent = redisTemplate.opsForValue().setIfAbsent("product:lock", 1);
                if (ifAbsent) {
                    try {
                        System.out.println("查询数据库......");
                        // 模拟从数据库查询数据
                        products = new ArrayList<Product>();
                        products.add(new Product(1, "商品1"));
                        products.add(new Product(2, "商品2"));
                        int i = 10 / 0;
                        redisTemplate.opsForValue().set("product:", products);
                    } finally {
                        redisTemplate.delete("product:lock");
                    }
                } else {
                    try {
                        Thread.sleep(1);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    cacheTest();
                }
            } else {
                System.out.println("查询缓存......");
            }
        }
    
        @Test
        public void delCacheTest() {
            redisTemplate.delete("product:");
        }
    }

**四、解决缓存击穿问题：**

原因：重复查询为null时，每次都会重新访问数据库；

解决：查询到为null值时，返回一个空的对象给redis作为缓存，设置一定时间失效；

@RunWith(SpringRunner.class)
    @SpringBootTest
    public class RedistestSpringData2ApplicationTests {
        @Autowired
        private RedisTemplate redisTemplate;
    
        public Product productById(Integer id) {
            if (id > 10) {
                return null;
            }
            return new Product();
        }
    
        @Test
        public void cachePenetrationTest() {
            for (int i = 11; i < 20; i++) {
                Product product = (Product) redisTemplate.opsForValue().get("product:" + i);
                if (product == null) {
                    // 模拟从数据库查询数据
                    System.out.println("查询数据库......");
                    // 如果i大于10，type都是null
                    product = productById(i);
                    // 如果时null返回一个空
                    if (product == null) {
                        product = new Product(i, "");
                        redisTemplate.opsForValue().set("product:" + i, product);
                        redisTemplate.expire("product:" + i, 10, TimeUnit.MINUTES);
                    } else {
                        redisTemplate.opsForValue().set("product:" + i, product);
                        redisTemplate.expire("product:" + i, 20, TimeUnit.MINUTES);
                    }
                } else {
                    System.out.println("查询缓存......");
                }
            }
        }
    
        @Test
        public void delCacheTest() {
            redisTemplate.delete("product:");
        }
    }

转载于:https://www.cnblogs.com/Tractors/p/11304252.html

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