redis.org

Redis is an in-memory non-relational database.

• Values are stored as key/value pairs which can be lists, hashes, blob, json etc. They’re volatile as they’re held in memory.
• The storage size is restricted by the ammount of RAM available.
• It’s significantly faster than a relational database at fetching data, making it quite useful for cache mechanisms.

A technique for keeping persisent data is often used where you store relevant information after a session ends in a relational database, then load it back once another session begins.

Every lang has a redis lib, example with Golang:

import (
    "context"
    "github.com/go-redis/redis/v8"
)

var ctx = context.Background()

func ExampleClient() {
    rdb := redis.NewClient(&redis.Options{
        Addr:     "localhost:6379",
        Password: "", // no password set
        DB:       0,  // use default DB
    })

    err := rdb.Set(ctx, "key", "value", 0).Err()
    if err != nil {
        panic(err)
    }

    val, err := rdb.Get(ctx, "key").Result()
    if err != nil {
        panic(err)
    }
    fmt.Println("key", val)

    val2, err := rdb.Get(ctx, "key2").Result()
    if err == redis.Nil {
        fmt.Println("key2 does not exist")
    } else if err != nil {
        panic(err)
    } else {
        fmt.Println("key2", val2)
    }
    // Output: key value
    // key2 does not exist
}