在用mysql客户端对数据库进行操作时，打开终端窗口，如果一段时间没有操作，再次操作时，常常会报如下错误：
ERROR (HY000): Lost connection to MySQL server during query
ERROR (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，连接的时长是如何确认的？
其实，这个与interactive_timeout和wait_timeout的设置有关。
首先，看看官方文档对于这两个参数的定义
interactive_timeout
默认是28800，单位秒，即8个小时
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.
wait_timeout
默认同样是28800s
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.
根据上述定义，两者的区别显而易见
1> 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客户端连接数据库是交互式连接，通过jdbc连接数据库是非交互式连接。
2> 在连接启动的时候，根据连接的类型，来确认会话变量wait_timeout的值是继承于全局变量wait_timeout，还是interactive_timeout。
下面来测试一下，确认如下问题
1. 控制连接最大空闲时长的是哪个参数。
2. 会话变量wait_timeout的继承问题
Q1：控制连接最大空闲时长的是哪个参数
A1：wait_timeout
验证
只修改wait_timeout参数
mysql> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 28800 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.03 sec)
mysql> set session WAIT_TIMEOUT=10;
Query OK, 0 rows affected (0.00 sec)
-------等待10s后再执行
mysql> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
ERROR 2013 (HY000): Lost connection to MySQL server during query
可以看到，等待10s后再执行操作，连接已经断开。
只修改interactive_timeout参数
mysql> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 28800 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.06 sec)
mysql> set session INTERACTIVE_TIMEOUT=10;
Query OK, 0 rows affected (0.00 sec)
----------等待10s后执行
mysql> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 10 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.06 sec)
Q2：会话变量wait_timeout的继承问题
A2：如果是交互式连接，则继承全局变量interactive_timeout的值，如果是非交互式连接，则继承全局变量wait_timeout的值。
验证：
只修改全局变量interactive_timeout的值
mysql> select variable_name,variable_value from information_schema.global_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 28800 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.13 sec)
mysql> set global INTERACTIVE_TIMEOUT=10;
Query OK, 0 rows affected (0.00 sec)
mysql> select variable_name,variable_value from information_schema.global_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_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> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 10 |
| WAIT_TIMEOUT | 10 |
+---------------------+----------------+
2 rows in set (0.00 sec)
发现，WAIT_TIMEOUT的值已经变为10了。
但通过jdbc测试，wait_timeout的值依旧是28800
public class Jdbc_test {
@SuppressWarnings("static-access")
public static void main(String[] args) throws Exception {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
String url = "jdbc:mysql://192.168.244.10:3306/test";
String user = "root";
String password = "123456";
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, user, password);
stmt = conn.createStatement();
String sql = "select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout')";
rs = stmt.executeQuery(sql);
while (rs.next()) {
System.out
.println(rs.getString(1)+": "+rs.getString(2));
}
}
}
结果输出如下：
INTERACTIVE_TIMEOUT: 10
WAIT_TIMEOUT: 28800
只修改全局变量wait_timeout的值
mysql> select variable_name,variable_value from information_schema.global_variables where variable_name in ('interactive_timeout','wa
it_timeout');+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 28800 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.17 sec)
mysql> set global WAIT_TIMEOUT=20;
Query OK, 0 rows affected (0.07 sec)
mysql> select variable_name,variable_value from information_schema.global_variables where variable_name in ('interactive_timeout','wa
it_timeout');+---------------------+----------------+
| variable_name | variable_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> select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout');
+---------------------+----------------+
| variable_name | variable_value |
+---------------------+----------------+
| INTERACTIVE_TIMEOUT | 28800 |
| WAIT_TIMEOUT | 28800 |
+---------------------+----------------+
2 rows in set (0.03 sec)
WAIT_TIMEOUT的值依旧是28800.
查看jdbc的结果
public class Jdbc_test {
@SuppressWarnings("static-access")
public static void main(String[] args) throws Exception {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
String url = "jdbc:mysql://192.168.244.10:3306/test";
String user = "root";
String password = "123456";
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, user, password);
stmt = conn.createStatement();
String sql = "select variable_name,variable_value from information_schema.session_variables where variable_name in ('interactive_timeout','wait_timeout')";
rs = stmt.executeQuery(sql);
while (rs.next()) {
System.out
.println(rs.getString(1)+": "+rs.getString(2));
}
Thread.currentThread().sleep(21000);
sql = "select 1 from dual";
rs = stmt.executeQuery(sql);
while (rs.next()) {
System.out
.println(rs.getInt(1));
}
}
}
查看jdbc的结果
INTERACTIVE_TIMEOUT: 28800
WAIT_TIMEOUT: 20
同时，新增了一段程序，等待20s后，再次执行查询，报如下错误：
Exception in thread "main" com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure Last packet sent to the server was 12 ms ago.
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3009)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2895)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3438)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1951)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2548)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2477)
at com.mysql.jdbc.StatementImpl.executeQuery(StatementImpl.java:1422)
at com.victor_01.Jdbc_test.main(Jdbc_test.java:29)
Caused by: java.net.SocketException: Software caused connection abort: recv failed
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.socketRead(Unknown Source)
at java.net.SocketInputStream.read(Unknown Source)
at java.net.SocketInputStream.read(Unknown Source)
at com.mysql.jdbc.util.ReadAheadInputStream.fill(ReadAheadInputStream.java:113)
at com.mysql.jdbc.util.ReadAheadInputStream.readFromUnderlyingStreamIfNecessary(ReadAheadInputStream.java:160)
at com.mysql.jdbc.util.ReadAheadInputStream.read(ReadAheadInputStream.java:188)
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2452)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2906)
... 8 more
总结
1. 控制连接最大空闲时长的wait_timeout参数。
2. 对于非交互式连接，类似于jdbc连接，wait_timeout的值继承自服务器端全局变量wait_timeout。
对于交互式连接，类似于mysql客户单连接，wait_timeout的值继承自服务器端全局变量interactive_timeout。
3. 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 | 192.168.244.20:44641 | NULL | Sleep | 1154 | | NULL |
+----+------+----------------------+------+---------+------+-------+------------------+
2 rows in set (0.03 sec)
参考
1. http://www.cnblogs.com/cenalulu/archive/2012/06/20/2554863.html