MySQL returning "Too many connections" error - mysql

Question

I'm doing something like this:
import(
"database/sql"
"github.com/go-sql-driver/mysql"
)
var db *sql.DB
func main() {
var err error
db, err = sql.Open(...)
if err != nil {
panic(err)
}
for j := 0; j < 8000; j++ {
_, err := db.Query("QUERY...")
if err != nil {
logger.Println("Error " + err.Error())
return
}
}
}
It works for the first 150 queries (for that I'm using another function to make) but after that, I get the error :
mysqli_real_connect(): (HY000/1040): Too many connections
So clearly I'm doing something wrong but I can't find what is it. I don't know what to open and close a new connection for each query.
Error in the log file :
"reg: 2020/06/28 03:35:34 Errores Error 1040: Too many connections"
(it is printed only once)
Error in mysql php my admin:
"mysqli_real_connect(): (HY000/1040): Too many connections"
"La conexión para controluser, como está definida en su configuración, fracasó."
(translated: "the connection for controluser, as it is defined in ti's configuration , failed.")
"mysqli_real_connect(): (08004/1040): Too many connections"

Answer 1

Every time you call Query(), you're creating a new database handle. Each active handle needs a unique database connection. Since you're not calling Close, that handle, and thus the connection, remains open until the program exits.
Solve your problem by calling rows.Close() after you're done with each query:
for j := 0; j < 8000; j++ {
rows, err := db.Query("QUERY...")
if err != nil {
logger.Println("Error " + err.Error())
return
}
// Your main logic here
rows.Close()
}
This Close() call is often called in a defer statement, but this precludes the use of a for loop (since a defer only executes when then function returns), so you may want to move your main logic to a new function:
for j := 0; j < 8000; j++ {
doStuff()
}
// later
func doStuff() {
rows, err := db.Query("QUERY...")
if err != nil {
logger.Println("Error " + err.Error())
return
}
defer rows.Close()
// Your main logic here
}