Golang上每次全局数据库连接与每次打开连接之间的性能差异

In my current project I was opening a new database connection every time when user makes request. For example:

func login(w http.ResponseWriter, r *http.Request) {

...

db, err := sqlx.Connect("postgres", "user=postgres password=*** dbname=postgres")

if err != nil {
    ErrorWithJSON(w, err.Error(), http.StatusBadRequest)
    return
}

db.SetMaxIdleConns(0)
db.SetConnMaxLifetime(time.Second * 30)

user, err := loginManager(db, m)

...

err = db.Close()

}

When I searched for other people's code, I've seen that most of the developers create a global variable for database connection, set it on the main and use this variable on entire project.

I was wondering is there any difference between these approaches? If I use global variable will there be any latency when 5 different users makes requests for register/login etc. If there will be latency, should I create multiple database connections and store them in a slice for future requests so I can pick randomly when users make request. Like a simple load balancer, I don't know?

Sorry for multiple questions. Thank you!