在用mysql客户端对数据库进行操作时，如果一段时间没有操作，再次操作时，常常会报如下错误：
ERROR 2013 (HY000): Lost connection to MySQL server during query
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
这个报错信息就意味着当前的连接已经断开，需要重新建立连接。
那么，连接建立后，连接的时长是如何确定的呢？
在MySQL中，这个与两个参数interactive_timeout和wait_timeout的设置有关。
注:以下说明基于MySQL 5.7.
1.interactive_timeout和wait_timeout的定义
首先，看看官方文档对于这两个参数的定义。
interactive_timeout
The number of seconds the server waits for activity on an interactive connection before closing it. An interactive client is defined as a client that uses the CLIENT_INTERACTIVE option to mysql_real_connect(). See also wait_timeout.
interactive_timeout参数，定义了对于交互式连接，服务端等待数据的最大时间。如果超过这个时间，服务端仍然没有收到数据，则会关闭连接。
所谓交互式client，是指调用mysql_real_connect()函数建立连接时，设置了CLIENT_INTERACTIVE选项。比较常用的就是命令行终端。
查看interactive_timeout的值：
mysql> show global variables like \'interactive_timeout%\';
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
+---------------------+-------+
1 row in set (0.01 sec)
默认是28800，单位秒，即8个小时
wait_timeout
The number of seconds the server waits for activity on a noninteractive connection before closing it.
On thread startup, the session wait_timeout value is initialized from the global wait_timeout value or from the global interactive_timeout value, depending on the type of client (as defined by the CLIENT_INTERACTIVE connect option to mysql_real_connect()). See also interactive_timeout.
wait_timeout参数，定义对于非交互式连接，服务端等待数据的最长时间。如果超过这个时间，服务端仍然没有收到数据，则会关闭连接。
在连接线程启动的时候，根据连接的类型，决定会话级的wait_timeout的值是初始化为全局的wait_timeout，还是全局的interactive_timeout。即如果是交互式连接，会话变量wait_timeout初始化为全局的interactive_timeout，否则，初始化为全局的wait_timeout。
查看wait_timeout的值：
mysql> show global variables like \'wait_timeout%\';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout | 28800 |
+---------------+-------+
1 row in set (0.00 sec)
默认同样是28800s,即8小时。
根据上述定义，两者的区别显而易见：interactive_timeout针对交互式连接，wait_timeout针对非交互式连接。所谓的交互式连接，即在mysql_real_connect()函数中使用了CLIENT_INTERACTIVE选项。
说得直白一点，通过mysql命令行终端连接数据库是交互式连接，通过jdbc等连接数据库是非交互式连接。
下面来测试一下，确认如下问题：
- 控制连接最大空闲时长的是哪个参数。
- 会话变量wait_timeout的继承问题
2.控制连接最大空闲时长的是哪个参数
先给出答案：wait_timeout
接下来进行验证。
2.1 只修改会话的wait_timeout参数
查看当前会话的wait_timeout和interactive_timeout。
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
设置当前会话的wait_timeout为10s
mysql> set session wait_timeout=10;
Query OK, 0 rows affected (0.00 sec)
再次查看
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 10 |
+---------------------+-------+
2 rows in set (0.00 sec)
等待10s，再次查看
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 8
Current database: *** NONE ***
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.01 sec)
可以看到，等待10s后再执行操作，原来的连接已经断开，并重新建立连接。
2.2 只修改会话的interactive_timeout参数
首先查看当前会话的interactive_timeout和wait_timeout.
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
接着，设置当前会话的interactive_timeout为10s
mysql> set session interactive_timeout=10;
Query OK, 0 rows affected (0.00 sec)
再次查看
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 10 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.01 sec)
等待10s，再次查看
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 10 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
可以看到，即使等待10后，连接是正常的。所以，设置interactive_timeout，对连接的时长没有影响。
3.会话变量wait_timeout的继承问题
上面已经提到，如果是交互式连接，则继承自全局变量interactive_timeout的值，如果是非交互式连接，则继承自全局变量wait_timeout的值。
下面进行验证。
3.1 只修改全局变量interactive_timeout的值
首先查看全局的interactive_timeout和wait_timeout。
mysql> show global variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
接着，设置全局的interactive_timeout为10s。
mysql> set global INTERACTIVE_TIMEOUT=10;
Query OK, 0 rows affected (0.00 sec)
再次查看
mysql> show global variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 10 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
开启另外一个MySQL客户端，查看会话变量的值：
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 10 |
| wait_timeout | 10 |
+---------------------+-------+
2 rows in set (0.01 sec)
发现，WAIT_TIMEOUT的值已经变为10了。
等待10s后，再次查看，会发现原来的连接已经断开，连接的时长设置已经生效。
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
Connection id: 70
Current database: *** NONE ***
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 10 |
| wait_timeout | 10 |
+---------------------+-------+
2 rows in set (0.01 sec)
但通过非终端测试，wait_timeout的值依旧是28800：
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 mysqlInit() {
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() {
mysqlInit()
execSql()
}
func execSql() {
var variableName string
var value int
sql := "show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\')"
rows, err := DB.Query(sql)
if err != nil {
log.Println("query failed:", err)
return
}
defer rows.Close()
for rows.Next() {
err = rows.Scan(&variableName, &value)
if err != nil {
log.Println("rows.Scan failed:", err)
return
}
log.Println("variable_name:", variableName, ", value:", value)
}
}
output:
2019/10/13 17:11:22 variable_name: interactive_timeout , value: 10
2019/10/13 17:11:22 variable_name: wait_timeout , value: 28800
结果输出如下
INTERACTIVE_TIMEOUT: 10
WAIT_TIMEOUT: 28800
3.2 只修改全局变量wait_timeout的值
首先查看全局的interactive_timeout和wait_timeout。
mysql> show global variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
接着，将全局的WAIT_TIMEOUT设置为20s。
mysql> set global WAIT_TIMEOUT=20;
Query OK, 0 rows affected (0.07 sec)
再次查看
mysql> show global variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 20 |
+---------------------+-------+
2 rows in set (0.00 sec)
开启另外一个mysql客户端，查看会话变量的值
mysql> show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\');
+---------------------+-------+
| Variable_name | Value |
+---------------------+-------+
| interactive_timeout | 28800 |
| wait_timeout | 28800 |
+---------------------+-------+
2 rows in set (0.00 sec)
WAIT_TIMEOUT的值依旧是28800.
查看非终端的代码执行的结果：
func execSql() {
var variableName string
var value int
sql := "show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\')"
rows, err := DB.Query(sql)
if err != nil {
log.Println("query failed:", err)
return
}
defer rows.Close()
for rows.Next() {
err = rows.Scan(&variableName, &value)
if err != nil {
log.Println("rows.Scan failed:", err)
return
}
log.Println("variable_name:", variableName, ", value:", value)
}
}
output:
2019/10/13 17:23:10 variable_name: interactive_timeout , value: 28800
2019/10/13 17:23:10 variable_name: wait_timeout , value: 20
修改程序，执行sql语句后，等待25s后，再次执行sql语句，查看执行情况。
func main() {
mysqlInit()
for {
execSql()
time.Sleep(25*time.Second)
}
}
func execSql() {
var variableName string
var value int
sql := "show session variables where Variable_name in (\'interactive_timeout\', \'wait_timeout\')"
rows, err := DB.Query(sql)
if err != nil {
log.Println("query failed:", err)
return
}
defer rows.Close()
for rows.Next() {
err = rows.Scan(&variableName, &value)
if err != nil {
log.Println("rows.Scan failed:", err)
return
}
log.Println("variable_name:", variableName, ", value:", value)
}
}
output:
2019/10/13 17:26:46 variable_name: interactive_timeout , value: 28800
2019/10/13 17:26:46 variable_name: wait_timeout , value: 20
[mysql] 2019/10/13 17:27:11 packets.go:36: unexpected EOF
[mysql] 2019/10/13 17:27:11 packets.go:141: write tcp 127.0.0.1:53878->127.0.0.1:3306: write: broken pipe
2019/10/13 17:27:11 variable_name: interactive_timeout , value: 28800
2019/10/13 17:27:11 variable_name: wait_timeout , value: 20
可以看到，等待25s后，再次执行sql，此时连接已经断开。
底层又重新建立连接。
4.总结
-
控制连接最大空闲时长的wait_timeout参数。
-
关于wait_timeout的继承
- 对于非交互式连接，类似于jdbc连接，wait_timeout的值继承自全局变量wait_timeout。
- 对于交互式连接，类似于mysql命令行终端，wait_timeout的值继承全局变量interactive_timeout。
-
判断一个连接的空闲时间，可通过show processlist输出中Sleep状态的时间
mysql> show processlist;
+----+------+----------------------+------+---------+------+-------+------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------+----------------------+------+---------+------+-------+------------------+
| 2 | root | localhost | NULL | Query | 0 | init | show processlist |
| 6 | repl | 192.132.2.66:56001 | NULL | Sleep | 1201 | | NULL |
+----+------+----------------------+------+---------+------+-------+------------------+
2 rows in set (0.03 sec)
5.参考
https://www.cnblogs.com/ivictor/p/5979731.html
http://www.cnblogs.com/cenalulu/archive/2012/06/20/2554863.html