3.6 Redis hotkey

This is a historical learning note and may contain outdated or incomplete understanding.

1. What Is a Redis Hot Key?

A key whose read/write QPS exceeds the QPS bottleneck of a single Redis instance. Because it is a single key, Redis Cluster cannot distribute the pressure.

2. How to Discover a Redis Hot Key

Business-service metrics reporting.
Redis proxy information collection.

A key accessed more than 10K times per second is considered a hot key.

3. How to Solve a Redis Hot Key

3.1. Replicate the Key

Add a random number suffix to the key and distribute the copies across different Redis instances. Read-through caching is generally used.

// Number of Redis instances
const M = 16

// Multiple of the number of Redis instances (designed as needed, 2^n times, where n is generally an integer from 1 to 4)
const N = 2

func main() {
// Get a Redis instance
    c, err := redis.Dial("tcp", "127.0.0.1:6379")
    if err != nil {
        fmt.Println("Connect to redis error", err)
        return
    }
    defer c.Close()

    hotKey := "hotKey:abc"
    // Random number
    randNum := GenerateRangeNum(1, N*M)
    // Get a dispersed key for the hot key
    tmpHotKey := hotKey + "_" + strconv.Itoa(randNum)

    // Hot-key expiration time
    expireTime := 50

    // A random time value used to smooth the expiration time
    randExpireTime := GenerateRangeNum(0, 5)

    data, err := redis.String(c.Do("GET", tmpHotKey))
    if err != nil {
        data, err = redis.String(c.Do("GET", hotKey))
        if err != nil {
            data = GetDataFromDb()
            c.Do("SET", "hotKey", data, expireTime)
            c.Do("SET", tmpHotKey, data, expireTime + randExpireTime)
        } else {
            c.Do("SET", tmpHotKey, data, expireTime + randExpireTime)
        }
    }
}

In essence, this is replication. It can only solve read-performance problems, not write problems, and its readability is poor.

3.2. Local Cache

Each machine replicates a copy of the Redis hot key, with load balancing. In essence, this is also replication. It can solve the read problem and can also solve the write problem (with consistent-hash routing to the same node).

1. What Is a Redis Hot Key?

2. How to Discover a Redis Hot Key

3. How to Solve a Redis Hot Key

3.1. Replicate the Key

3.2. Local Cache

4. References

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