Go Mysql connection refused due to a burst of connections - mysql

Question

Go version 1.18. MySQL server is version 8. System is 2018 MacBook Pro i9 6-cores, 32GB RAM.
However, mysql connection is refused during mysql.QueryRow(). error message is:
panic: dial unix /tmp/mysql.sock: connect: connection refused
PLEASE NOTE: I already find root cause(see my comment in the following code) and have a solution(using semaphore).
I MUST use socket instead of localhost when setting db connection.
The root cause is 2000 Go routines try to send query to MySQL simultaneously. How to solve this problem? My solution is to use semaphore to limit the number of concurrent go-routines, for example 100. I have tested, semaphore solution works well. I actually do not want to use semaphore to limit the number of concurrent mysql queries.
Question: why I can not have 2000 go-routines sending query at the same time.
import (
"database/sql"
mysqlDriver "github.com/go-sql-driver/mysql"
)
type SomeStruct struct {
a string
b string
}
func main() {
cfg := mysqlDriver.Config{
User: "DB_USER",
Passwd: "DB_USER",
Net: "unix",
Addr: "/tmp/mysql.sock", // MySQL is installed on local
DBName: "databaseName",
}
mysql, err := sql.Open("mysql", cfg.FormatDSN())
if err != nil {
panic(err) // tested, panic is not caused here.
}
mysql.SetMaxOpenConns(5000)
mysql.SetMaxIdleConns(5000)
if err = mysql.Ping(); err != nil {
panic(err) // tested, panic is not caused here.
}
var wg sync.WaitGroup
for i := 0; i < 2000; i++ {
wg.Add(1)
go func() {
defer wg.Done()
var someStructVar SomeStruct
err := mysql.QueryRow("select a, b from table where id = ?", i).Scan(&someStructVar.a, &someStructVar.b)
if err != nil {
panic(err) // this is where the panic happens.
}
}
}
wg.Wait()
}
my.cnf is:
[mysqld]
max_connections=5000
connect_timeout=300

Answer 1

If your panic error occur before code
mysql.SetMaxOpenConns(5000)
Then the error is when connecting to the database, try changing the connection configuration to the database