如何在golang中设置提取大小？

Question

I am trying to load a huge data set from DB.

    func main() {
        db, err := sql.Open("mysql", "root:pass1@tcp(127.0.0.1:3306)/tuts")

        if err != nil {
            log.Print(err.Error())
        }
        defer db.Close()
        results, err := db.Query("SELECT id, name FROM tags")
        if err != nil {
            panic(err.Error()) 
        }

        for results.Next() {
            var tag Tag
            err = results.Scan(&tag.ID, &tag.Name)
            if err != nil {
                panic(err.Error()) 
            }

            log.Printf(tag.Name)
        }
}

Does the program load all the records to memory in single shot? Or is there any way to specify the fetch size so that program will load only n of rows at a time? Assuming there are million rows in the database, i would like to fetch 1000 records each time.

Answer 1

This will work just fine for a single row and millions of rows. Most SQL implementations have the notion of batches when reading. They load data from the disk as needed and keeps RAM usage low/constant as needed.

For example if you are selecting 1000 rows. The database may load the first 100 rows to the RAM. While you are calling Next(), for example when you reach the 50th row, the database grabs another hundred (rows 100 to 201 for example).