This paper test the connection timeout mysql.
Here the "connection" is meant to establish the connection.
Mysql connection timeout is set by the timeout parameter.
1. Establish a connection timeout test
In the following example, provided for the connection time 5s.
MySQL server IP is 192.168.0.101, port 3306.
3s performed once per SQL.
// simple.go
package main
import (
"database/sql"
"log"
"time"
_ "github.com/go-sql-driver/mysql"
)
var DB *sql.DB
var dataBase = "root:Aa123456@tcp(192.168.0.101:3306)/?timeout=5s&readTimeout=6s"
func mysqlInit() {
var err error
DB, err = sql.Open("mysql", dataBase)
if err != nil {
log.Fatalln("open db fail:", err)
}
DB.SetMaxOpenConns(3)
DB.SetMaxIdleConns(3)
}
func main() {
mysqlInit()
for {
log.Println("start")
execSql()
time.Sleep(3*time.Second)
}
}
func execSql() {
var value int
err := DB.QueryRow("select 1").Scan(&value)
if err != nil {
log.Println("query failed:", err)
return
}
log.Println("value:", value)
}starting program:
go run simple.goAfter then use iptables to send all packets to MySQL service drop off:
sudo iptables -A OUTPUT -p tcp --dport 3306 -d 192.168.0.101 -j DROP
This will trigger a retry mechanism, last time out.
output:
2019/10/27 18:34:52 start
2019/10/27 18:34:52 value: 1
2019/10/27 18:34:55 start
2019/10/27 18:34:55 value: 1
2019/10/27 18:34:58 start
2019/10/27 18:34:58 value: 1
2019/10/27 18:35:01 start
[mysql] 2019/10/27 18:35:07 packets.go:36: read tcp 192.168.0.104:54462->192.168.0.101:3306: i/o timeout
2019/10/27 18:35:07 query failed: invalid connection
2019/10/27 18:35:10 start
[mysql] 2019/10/27 18:35:15 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:35:20 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
2019/10/27 18:35:20 query failed: driver: bad connection
2019/10/27 18:35:23 start
[mysql] 2019/10/27 18:35:28 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:35:33 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:35:38 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
2019/10/27 18:35:38 query failed: driver: bad connection
2019/10/27 18:35:41 start
[mysql] 2019/10/27 18:35:46 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:35:51 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:35:56 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
2019/10/27 18:35:56 query failed: driver: bad connection
2019/10/27 18:35:59 start
[mysql] 2019/10/27 18:36:04 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:36:09 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
[mysql] 2019/10/27 18:36:14 driver.go:81: net.Error from Dial()': dial tcp 192.168.0.101:3306: i/o timeout
2019/10/27 18:36:14 query failed: driver: bad connection
You can see from the output every time you perform SQL, there are three connection error log indicates a connection, it will try three times (timeout that is set) timeout 5s.
Here it begs the question, why every time SQL execution, will be conducted three times a connection attempt it?
Check QueryRowthe underlying implementation code:
func (db *DB) QueryRow(query string, args ...interface{}) *Row {
return db.QueryRowContext(context.Background(), query, args...)
}
func (db *DB) QueryRowContext(ctx context.Context, query string, args ...interface{}) *Row {
rows, err := db.QueryContext(ctx, query, args...)
return &Row{rows: rows, err: err}
}
// QueryContext executes a query that returns rows, typically a SELECT.
// The args are for any placeholder parameters in the query.
func (db *DB) QueryContext(ctx context.Context, query string, args ...interface{}) (*Rows, error) {
var rows *Rows
var err error
for i := 0; i < maxBadConnRetries; i++ {
rows, err = db.query(ctx, query, args, cachedOrNewConn)
if err != driver.ErrBadConn {
break
}
}
if err == driver.ErrBadConn {
return db.query(ctx, query, args, alwaysNewConn)
}
return rows, err
}Wherein, maxBadConnRetries 2 is defined as:
// maxBadConnRetries is the number of maximum retries if the driver returns
// driver.ErrBadConn to signal a broken connection before forcing a new
// connection to be opened.
const maxBadConnRetries = 2When err is driver.ErrBadConnwhen will try three times to connect. That's why just log in three times a connection error.
2.reject test
In addition, if you use iptables will all be sent to the MySQL server packets reject out:
sudo iptables -A OUTPUT -p tcp --dport 3306 -d 192.168.0.101 -j REJECTRESET operation will be returned directly reject the connection reset, it does not trigger connection establishment timeout.
Log output:
2019/10/27 21:39:55 start
2019/10/27 21:39:55 value: 1
2019/10/27 21:39:58 start
2019/10/27 21:39:58 value: 1
2019/10/27 21:40:01 start
2019/10/27 21:40:01 value: 1
2019/10/27 21:40:04 start
2019/10/27 21:40:04 value: 1
2019/10/27 21:40:07 start
[mysql] 2019/10/27 21:40:13 packets.go:36: read tcp 192.168.0.104:54536->192.168.0.101:3306: i/o timeout
2019/10/27 21:40:13 query failed: invalid connection
2019/10/27 21:40:16 start
2019/10/27 21:40:17 query failed: dial tcp 192.168.0.101:3306: connect: connection refused
2019/10/27 21:40:20 start
2019/10/27 21:40:21 query failed: dial tcp 192.168.0.101:3306: connect: connection refused
2019/10/27 21:40:24 start
2019/10/27 21:40:25 query failed: dial tcp 192.168.0.101:3306: connect: connection refused
2019/10/27 21:40:28 start
2019/10/27 21:40:29 query failed: dial tcp 192.168.0.101:3306: connect: connection refused
2019/10/27 21:40:32 start
2019/10/27 21:40:33 query failed: dial tcp 192.168.0.101:3306: connect: connection refused
3. References
golang database sql DSN (Data Source Name)中的timeout, readTimeout