[redis] ③ data elimination strategy, pipeline command, publish and subscribe

One 、 Data elimination strategy

Redis The biggest reason why it is fast is ： It stores data in Memory In . The capacity of memory is incomparable with that of hard disk , The memory capacity will always reach the maximum . When the memory capacity reaches a certain value, you need to correct Redis Delete the data stored in memory （ Eliminate ） operation , Delete those data ？ When to delete ？

stay Redis in , Allows the user to set the maximum memory size （Redis The maximum capacity of data that can be stored ）【 stay Redis Configuration in the configuration file of 】
maxmemory 1G
maxmemory-policy noeviction # No elimination strategy , beyond 1G Report errors

lft： according to key Use frequency To eliminate
lru： according to key Recent use of Time To eliminate

• volatile-lru： Set the timeout time in the data , Delete the least commonly used data
• allkeys-lru： all key Delete the least frequently used data in
• volatile-random： Delete randomly in the data with timeout set
• allkeys-random： be-all key Randomly delete
• volatile-ttl： Query all set timeout data , Then sort it immediately , Delete the data that is about to expire
• noeviction： Delete operation will not be performed , If the memory overflows, an error is reported
• volatile-lfu： Expel the least frequently used key from all keys configured with expiration time
• allkeys-lfu： Eject the least frequently used key from all keys

Two 、Java Basic use Redis（Jedis）

    <dependencies>
        <dependency>
            <groupId>redis.clients</groupId>
            <artifactId>jedis</artifactId>
            <version>3.1.0</version>
        </dependency>  
    </dependencies> 

public class BasicTest {
    
    private Jedis jedis;

    @Before
    public void init() {
    
        jedis = new Jedis("192.168.80.130", 6379);
    }

    @Test
    public void test1() {
    
        jedis.flushAll();
        System.out.println(jedis.dbSize());
    }

    @After
    public void destroy() {
    
        if (jedis != null)
            jedis.close();
    }

}

3、 ... and 、pipeline

• Put the command into the pipeline , Bulk send to Redis Server side , Improve performance , Greatly reduce network consumption
• There is no connection between commands executed in batches
• Not all data structures can be used pipeline command
• pipeline The operation of is not atomic
  

public class PipelineTest {
    
    private Jedis jedis;

    @Before
    public void init() {
    
        jedis = new Jedis("192.168.80.130", 6379);
    }

    @Test
    public void testPipeline() {
    
        Times.test(" Pipeline command is not used ", this::noPipeline);
        Times.test(" Use the pipeline command ", this::pipeline);
    }

    private void noPipeline() {
    
        for (int i = 0; i < 66666; i++) {
    
            jedis.set("no" + i, String.valueOf(i));
        }
    }

    private void pipeline() {
    
        //  Create pipes 
        Pipeline pipeline = jedis.pipelined();
        for (int i = 0; i < 66666; i++) {
    
            //  Add commands to the pipeline 
            pipeline.set("pipeline" + i, String.valueOf(i));
        }
        //  Synchronous execution of commands 
        pipeline.sync();
    }

    @After
    public void destroy() {
    
        if (jedis != null)
            jedis.close();
    }

}

Execution results ：

Four 、 Publish subscribe