set the maximum number of connections golang mysql

This article describes golang in connection MySQL, how to set the maximum number of connections.

An example is given package MySQL connection with the github.com/go-sql-driver/mysql.

Set the interface maximum number of connections is

func (db *DB) SetMaxOpenConns(n int) 

Sets the maximum number of connections MySQL can be opened.

If n <= 0, represents the number of open connections is not limited.

The default is 0, that is, does not limit the number of connections.

Another relevant parameter is the connection number MaxIdleConnsindicates the maximum number of idle connections.

If MaxIdleConnsgreater than 0, and greater than MaxOpenConns, and finally MaxIdleConnsthe last equal MaxOpenConns.

1. Test Examples

First, the maximum number of connections is provided for opening 1, and then turned 20 goroutine, each goroutine sql statement execution, and connected to the print execution sql connection id used. And time-consuming sql statement occupancy connection, observe the results.

package main

import (
        "database/sql"
        "log"

        _ "github.com/go-sql-driver/mysql"
)

var DB *sql.DB
var dataBase = "root:Aa123456@tcp(127.0.0.1:3306)/?loc=Local&parseTime=true"

func Init() {
        var err error
        DB, err = sql.Open("mysql", dataBase)
        if err != nil {
                log.Fatalln("open db fail:", err)
        }

        DB.SetMaxOpenConns(1)

        err = DB.Ping()
        if err != nil {
                log.Fatalln("ping db fail:", err)
        }
}

func main() {
        Init()

        for {
                for i:=0; i < 20; i++ {
                        go one_worker(i)
                }
                select {
                }
        }
}

func one_worker(i int) {
        var connection_id int
        err := DB.QueryRow("select CONNECTION_ID()").Scan(&connection_id)
        if err != nil {
                log.Println("query connection id failed:", err)
                return
        }

        log.Println("worker:", i, ", connection id:", connection_id)

        var result int
        err = DB.QueryRow("select sleep(10)").Scan(&result)
        if err != nil {
                log.Println("query sleep connection id faild:", err)
                return
        }

}

output

2019/10/02 18:14:25 worker: 2 , connection id: 55
2019/10/02 18:14:25 worker: 17 , connection id: 55
2019/10/02 18:14:25 worker: 11 , connection id: 55
2019/10/02 18:14:35 worker: 3 , connection id: 55
2019/10/02 18:14:45 worker: 0 , connection id: 55
2019/10/02 18:14:45 worker: 4 , connection id: 55
2019/10/02 18:14:45 worker: 5 , connection id: 55
2019/10/02 18:15:05 worker: 7 , connection id: 55
2019/10/02 18:15:25 worker: 15 , connection id: 55
2019/10/02 18:15:25 worker: 6 , connection id: 55
2019/10/02 18:15:35 worker: 13 , connection id: 55
2019/10/02 18:15:45 worker: 19 , connection id: 55
2019/10/02 18:15:45 worker: 10 , connection id: 55
2019/10/02 18:15:45 worker: 12 , connection id: 55
2019/10/02 18:15:55 worker: 14 , connection id: 55
2019/10/02 18:16:15 worker: 8 , connection id: 55
2019/10/02 18:16:35 worker: 18 , connection id: 55
2019/10/02 18:16:35 worker: 1 , connection id: 55
2019/10/02 18:17:05 worker: 16 , connection id: 55
2019/10/02 18:17:35 worker: 9 , connection id: 55

Can be seen from the output, goroutine 20 turns using a connection (connection id as 55) perform sql statement.

2. Check the connection

Use show processlist view connection

mysql> show processlist;
+----+------+-----------------+------+---------+------+------------+------------------+
| Id | User | Host            | db   | Command | Time | State      | Info             |
+----+------+-----------------+------+---------+------+------------+------------------+
| 20 | root | localhost       | NULL | Query   |    0 | starting   | show processlist |
| 55 | root | localhost:59518 | NULL | Query   |    5 | User sleep | select sleep(10) |
+----+------+-----------------+------+---------+------+------------+------------------+
2 rows in set (0.00 sec)

Use netstat see the connection

netstat -an | grep 3306
tcp4       0      0  127.0.0.1.3306         127.0.0.1.59518        ESTABLISHED
tcp4       0      0  127.0.0.1.59518        127.0.0.1.3306         ESTABLISHED
tcp46      0      0  *.3306                 *.*                    LISTEN

It can be seen only established a connection.