本文测试连接mysql的超时时间。
这里的“连接”是建立连接的意思。
连接mysql的超时时间是通过参数timeout设置的。
1.建立连接超时测试
下面例子中，设置连接超时时间为5s，读超时时间6s。
MySQL server IP是192.168.0.101，端口3306。
每3s执行一次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)
}
启动程序：
go run simple.go
之后，接着在客户端使用iptables将所有发送到MySQL服务的数据包drop掉.
清除所有的过滤规则，防止干扰:
sudo iptables -F
设置drop策略：
sudo iptables -A OUTPUT -p tcp --dport 3306 -d 192.168.0.101 -j DROP
查看策略：
[root@localhost lanyang]# iptables -nxvL
Chain INPUT (policy ACCEPT 4 packets, 505 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 4 packets, 304 bytes)
pkts bytes target prot opt in out source destination
49 3025 DROP tcp -- * * 0.0.0.0/0 192.168.0.101 tcp dpt:3306
或者在MySQL上设置iptables规则，效果是一样的：
sudo iptables -A INPUT -p tcp --dport 3306 -d 192.168.0.101 -j DROP
这样就会触发重试机制，最后超时。
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
从输出结果可以看到，首先打印读超时错误，6s超时(即readTimeout):
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
接着，每次执行SQL，都有3条连接错误日志，表示建立连接时，会尝试3次，每次超时时间5s(即设置的timeout)。
这里就引出一个问题，为什么每次执行SQL时，会进行3次建立连接尝试呢？
查一下QueryRow底层实现代码:
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
}
其中，maxBadConnRetries定义为2：
// 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 = 2
当err是driver.ErrBadConn时，会尝试3次进行连接。这就是为什么刚才的日志中有3次连接错误。
2.reject测试
另外，如果在客户端使用iptables将所有发送到MySQL服务的数据包reject掉:
sudo iptables -A OUTPUT -p tcp --dport 3306 -d 192.168.0.101 -j REJECT
sudo iptables -nxvL
Chain INPUT (policy ACCEPT 5 packets, 515 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 4 packets, 372 bytes)
pkts bytes target prot opt in out source destination
4 260 REJECT tcp -- * * 0.0.0.0/0 192.168.0.101 tcp dpt:3306 reject-with icmp-port-unreachable
或者在MySQL上设置iptables规则，效果是一样的：
sudo iptables -A INPUT -p tcp --dport 3306 -d 192.168.0.101 -j REJECT
2.1 测试1：timeout=5s&readTimeout=6s
此时，
reject会直接返回RESET操作，将连接重置，不会触发连接建立超时时间。
日志输出：
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
从输出中可以看到，首先打印读超时错误，读超时readTimeout设置为6s:
[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
后续的日志，都是连接被reset，无法连接的错误。
2.2 测试2：timeout=1s&readTimeout=6s
在测试结果表现上，与测试1基本相同。
唯一不同的是，有时会触发i/o timeout。
因为测试2中设置的timeout是1s，比测试1中timeout 5s小。
日志输出：
2020/03/29 16:35:09 start
2020/03/29 16:35:09 value: 1
2020/03/29 16:35:12 start
2020/03/29 16:35:12 value: 1
2020/03/29 16:35:15 start
[mysql] 2020/03/29 16:35:21 packets.go:36: read tcp 192.168.1.107:49654->192.168.1.107:3306: i/o timeout
2020/03/29 16:35:21 query failed: invalid connection
2020/03/29 16:35:24 start
[mysql] 2020/03/29 16:35:25 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:35:26 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:35:26 query failed: driver: bad connection
2020/03/29 16:35:29 start
2020/03/29 16:35:30 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:35:33 start
2020/03/29 16:35:34 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:35:37 start
2020/03/29 16:35:38 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:35:41 start
[mysql] 2020/03/29 16:35:42 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:35:43 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:35:46 start
[mysql] 2020/03/29 16:35:47 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:35:48 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:35:49 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:35:49 query failed: driver: bad connection
2020/03/29 16:35:52 start
[mysql] 2020/03/29 16:35:53 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:35:54 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:35:55 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:35:55 query failed: driver: bad connection
2020/03/29 16:35:58 start
[mysql] 2020/03/29 16:35:59 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:00 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:01 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:36:01 query failed: driver: bad connection
2020/03/29 16:36:04 start
[mysql] 2020/03/29 16:36:05 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:06 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:36:07 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:36:10 start
[mysql] 2020/03/29 16:36:11 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:12 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:36:13 query failed: dial tcp 192.168.1.107:3306: connect: connection refused
2020/03/29 16:36:16 start
[mysql] 2020/03/29 16:36:17 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:18 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
[mysql] 2020/03/29 16:36:19 driver.go:81: net.Error from Dial()': dial tcp 192.168.1.107:3306: i/o timeout
2020/03/29 16:36:19 query failed: driver: bad connection
3.参考
golang database sql DSN (Data Source Name)中的timeout, readTimeout
Just try, don't shy.
