duplicate operations cause by `maxBadConnRetries`

[yanghuashuai]

Issue description

duplicate operations cause by maxBadConnRetries cause by read timeout, source code:
github.com/go-sql-driver/mysql/packets.go

  23 // Packets documentation:
  24 // http://dev.mysql.com/doc/internals/en/client-server-protocol.html
  25
  26 // Read packet to buffer 'data'
  27 func (mc *mysqlConn) readPacket() ([]byte, error) {
  28     var prevData []byte
  29     for {
  30         // read packet header
  31         data, err := mc.buf.readNext(4)
  32         if err != nil {
  33             errLog.Print(err)
  34             mc.Close()
  35             return nil, driver.ErrBadConn
  36         }

As define in go/src/database/sql/driver/driver.go:

 65 // ErrBadConn should be returned by a driver to signal to the sql
 66 // package that a driver.Conn is in a bad state (such as the server
 67 // having earlier closed the connection) and the sql package should
 68 // retry on a new connection.
 69 //
 70 // To prevent duplicate operations, ErrBadConn should NOT be returned
 71 // if there's a possibility that the database server might have
 72 // performed the operation. Even if the server sends back an error,
 73 // you shouldn't return ErrBadConn.
 74 var ErrBadConn = errors.New("driver: bad connection")

So, why read timeout return ErrBadConn ?

Example code

package main

import (
    "database/sql"
    "fmt"

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

func main() {
    db, _ := sql.Open("mysql", "root:123456@tcp(10.94.99.247:3306)/mysql?charset=utf8&parseTime=True&loc=Local&timeout=200ms&readTimeout=1s&writeTimeout=200ms")
    _, err := db.Exec("select sleep(?)", 2)
    if err != nil {
        fmt.Println(err.Error())
    }
}

Error log

[mysql] 2017/05/02 17:29:32 packets.go:33: read tcp 10.97.212.42:50230->10.94.99.247:3306: i/o timeout
[mysql] 2017/05/02 17:29:33 packets.go:33: read tcp 10.97.212.42:50231->10.94.99.247:3306: i/o timeout
[mysql] 2017/05/02 17:29:34 packets.go:33: read tcp 10.97.212.42:50232->10.94.99.247:3306: i/o timeout
driver: bad connection

Configuration

Driver git SHA:
147bd02

Go version:
go version go1.8 darwin/amd64

Server version:
mysqld Ver 5.6.28 for Linux on x86_64 (MySQL Community Server (GPL))

Server OS:
Linux kvm36130.sg 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux

[julienschmidt]

See #302
We are aware of the problem but still looking for a sensible solution

[julienschmidt]

Should be fixed now since #302 is merged