Interview raids | how does redis query a key from massive data? Attached video

1. Review knowledge points

The knowledge points investigated in this topic are as follows:

2 solution ideas

3 keys usage related

1) Keys is used as follows

2) Problems with keys

4 scan usage related

Let's first simulate massive data and add 10W pieces of data using pipeline. The Java code is as follows:

import redis.clients.jedis.Jedis;
import redis.clients.jedis.Pipeline;
import utils.JedisUtils;

public class ScanExample {
    public static void main(String[] args) {
        // 添加 10w 条数据
        initData();
    }
    public static void initData(){
        Jedis jedis = JedisUtils.getJedis();
        Pipeline pipe = jedis.pipelined();
        for (int i = 1; i < 100001; i++) {
            pipe.set("user_token_" + i,"id" + i);
        }
        // 执行命令
        pipe.sync();
        System.out.println("数据插入完成");
    }
}

Let's query the data with user ID 9999 *. The scan command is as follows:

127.0.0.1:6379> scan 0 match user_token_9999* count 10000
1) "127064"
2) 1) "user_token_99997"
127.0.0.1:6379> scan 127064 match user_token_9999* count 10000
1) "1740"
2) 1) "user_token_9999"
127.0.0.1:6379> scan 1740 match user_token_9999* count 10000
1) "21298"
2) 1) "user_token_99996"
127.0.0.1:6379> scan 21298 match user_token_9999* count 10000
1) "65382"
2) (empty list or set)
127.0.0.1:6379> scan 65382 match user_token_9999* count 10000
1) "78081"
2) 1) "user_token_99998"
   2) "user_token_99992"
127.0.0.1:6379> scan 78081 match user_token_9999* count 10000
1) "3993"
2) 1) "user_token_99994"
   2) "user_token_99993"
127.0.0.1:6379> scan 3993 match user_token_9999* count 10000
1) "13773"
2) 1) "user_token_99995"
127.0.0.1:6379> scan 13773 match user_token_9999* count 10000
1) "47923"
2) (empty list or set)
127.0.0.1:6379> scan 47923 match user_token_9999* count 10000
1) "59751"
2) 1) "user_token_99990"
   2) "user_token_99991"
   3) "user_token_99999"
127.0.0.1:6379> scan 59751 match user_token_9999* count 10000
1) "0"
2) (empty list or set)

From the above implementation results, we can see two problems:

Related syntax: scan cursor [match pattern] [count count]

Of which:

5 scan code practice

In this article, we use java code to realize the query function of scan. The code is as follows:

import redis.clients.jedis.Jedis;
import redis.clients.jedis.Pipeline;
import redis.clients.jedis.ScanParams;
import redis.clients.jedis.ScanResult;
import utils.JedisUtils;

public class ScanExample {
    public static void main(String[] args) {
        Jedis jedis = JedisUtils.getJedis();
        // 定义 match 和 count 参数
        ScanParams params = new ScanParams();
        params.count(10000);
        params.match("user_token_9999*");
        // 游标
        String cursor = "0";
        while (true) {
            ScanResult<String> res = jedis.scan(cursor,params);
            if (res.getCursor().equals("0")) {
                // 表示最后一条
                break;
            }
            cursor = res.getCursor(); // 设置游标
            for (String item : res.getResult()) {
                // 打印查询结果
                System.out.println("查询结果：" + item);
            }
        }
    }
}

The results of the above procedures are as follows:

6 Summary

Through this article, we know that if redis wants to query a certain data in a large amount of data, scan should be used. Scan has the following characteristics:

7 video version

Video version: https://www.bilibili.com/video/av88076985/