在用MySQL客戶端對數據庫進行操作時,如果一段時間沒有操作,再次操作時,常常會報如下錯誤:
ERROR 2013 (HY000): Lost connection to MySQL server during query
ERROR 2006 (HY000): MySQL server has gone away
No connection. Trying to reconnect...
這個報錯信息就意味着當前的連接已經斷開,需要重新建立連接。
那麼,連接建立後,連接的時長是如何確定的呢?
在MySQL中,這個與兩個參數interactive_timeout
和wait_timeout
的設置有關。
注:以下說明基於MySQL 5.7.
1.interactive_timeout和wait_timeout的定義
首先,看看官方文檔對於這兩個參數的定義。
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參數,定義了對於交互式連接,服務端等待數據的最大時間。如果超過這個時間,服務端仍然沒有收到數據,則會關閉連接。
所謂交互式client,是指調用mysql_real_connect()函數建立連接時,設置了CLIENT_INTERACTIVE選項。比較常用的就是命令行終端。
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)
默認是28800,單位秒,即8個小時
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參數,定義對於非交互式連接,服務端等待數據的最長時間。如果超過這個時間,服務端仍然沒有收到數據,則會關閉連接。
在連接線程啓動的時候,根據連接的類型,決定會話級的wait_timeout的值是初始化爲全局的wait_timeout,還是全局的interactive_timeout。即如果是交互式連接,會話變量wait_timeout初始化爲全局的interactive_timeout,否則,初始化爲全局的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)
默認同樣是28800s,即8小時。
根據上述定義,兩者的區別顯而易見:interactive_timeout針對交互式連接,wait_timeout針對非交互式連接。所謂的交互式連接,即在mysql_real_connect()函數中使用了CLIENT_INTERACTIVE選項。
說得直白一點,通過mysql命令行終端連接數據庫是交互式連接,通過jdbc等連接數據庫是非交互式連接。
下面來測試一下,確認如下問題:
- 控制連接最大空閒時長的是哪個參數。
- 會話變量wait_timeout的繼承問題
2.控制連接最大空閒時長的是哪個參數
先給出答案:wait_timeout
接下來進行驗證。
2.1 只修改會話的wait_timeout參數
查看當前會話的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)
設置當前會話的wait_timeout爲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後再執行操作,原來的連接已經斷開,並重新建立連接。
2.2 只修改會話的interactive_timeout參數
首先查看當前會話的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,設置當前會話的interactive_timeout爲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後,連接是正常的。所以,設置interactive_timeout,對連接的時長沒有影響。
3.會話變量wait_timeout的繼承問題
上面已經提到,如果是交互式連接,則繼承自全局變量interactive_timeout的值,如果是非交互式連接,則繼承自全局變量wait_timeout的值。
下面進行驗證。
3.1 只修改全局變量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,設置全局的interactive_timeout爲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)
開啓另外一個MySQL客戶端,查看會話變量的值:
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)
發現,WAIT_TIMEOUT的值已經變爲10了。
等待10s後,再次查看,會發現原來的連接已經斷開,連接的時長設置已經生效。
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)
但通過非終端測試,wait_timeout的值依舊是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
結果輸出如下
INTERACTIVE_TIMEOUT: 10
WAIT_TIMEOUT: 28800
3.2 只修改全局變量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,將全局的WAIT_TIMEOUT設置爲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)
開啓另外一個mysql客戶端,查看會話變量的值
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的值依舊是28800.
查看非終端的代碼執行的結果:
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,執行sql語句後,等待25s後,再次執行sql語句,查看執行情況。
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後,再次執行sql,此時連接已經斷開。
底層又重新建立連接。
4.總結
-
控制連接最大空閒時長的wait_timeout參數。
-
關於wait_timeout的繼承
- 對於非交互式連接,類似於jdbc連接,wait_timeout的值繼承自全局變量wait_timeout。
- 對於交互式連接,類似於mysql命令行終端,wait_timeout的值繼承全局變量interactive_timeout。
-
判斷一個連接的空閒時間,可通過show processlist輸出中Sleep狀態的時間
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)
5.參考
https://www.cnblogs.com/ivictor/p/5979731.html
http://www.cnblogs.com/cenalulu/archive/2012/06/20/2554863.html
http://www.cnblogs.com/Alight/p/4118515.html
http://ronaldbradford.com/blog/sqlstatehy000-general-error-2006-mysql-server-has-gone-away-2013-01-02/