在用mysql客戶端對資料庫進行操作時，開啟終端視窗，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...

這個報錯資訊就意味著當前的連線已經斷開，需要重新建立連線。

那麼，連線的時長是如何確認的？

其實，這個與interactive_timeout和wait_timeout的設定有關。

首先，看看官方文件對於這兩個引數的定義

interactive_timeout

預設是28800，單位秒，即8個小時

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

默認同樣是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.

根據上述定義，兩者的區別顯而易見

1>interactive_timeout針對互動式連線，wait_timeout針對非互動式連線。所謂的互動式連線，即在mysql_real_connect()函式中使用了CLIENT_INTERACTIVE選項。

說得直白一點，通過mysql客戶端連線資料庫是互動式連線，通過jdbc連線資料庫是非互動式連線。

2> 在連線啟動的時候，根據連線的型別，來確認會話變數wait_timeout的值是繼承於全域性變數wait_timeout，還是interactive_timeout。

下面來測試一下，確認如下問題

1. 控制連線最大空閒時長的是哪個引數。

2. 會話變數wait_timeout的繼承問題

Q1：控制連線最大空閒時長的是哪個引數

A1：wait_timeout

驗證

只修改wait_timeout引數

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後再執行
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後再執行操作，連線已經斷開。

只修改interactive_timeout引數

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後執行
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：會話變數wait_timeout的繼承問題

A2：如果是互動式連線，則繼承全域性變數interactive_timeout的值，如果是非互動式連線，則繼承全域性變數wait_timeout的值。

驗證：

只修改全域性變數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)

開啟另外一個mysql客戶端，檢視會話變數的值

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)

發現，WAIT_TIMEOUT的值已經變為10了。

但通過jdbc測試，wait_timeout的值依舊是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));
         }
    }
}

結果輸出如下：

INTERACTIVE_TIMEOUT:  10
WAIT_TIMEOUT:  28800

只修改全域性變數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)

開啟另外一個mysql客戶端，檢視會話變數的值

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的值依舊是28800.

檢視jdbc的結果

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));
         }

    }
}

檢視jdbc的結果

INTERACTIVE_TIMEOUT:  28800
WAIT_TIMEOUT:  20

同時，新增了一段程式，等待20s後，再次執行查詢，報如下錯誤：

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

總結

1.控制連線最大空閒時長的wait_timeout引數。

2. 對於非互動式連線，類似於jdbc連線，wait_timeout的值繼承自伺服器端全域性變數wait_timeout。

對於互動式連線，類似於mysql客戶單連線，wait_timeout的值繼承自伺服器端全域性變數interactive_timeout。

3. 判斷一個連線的空閒時間，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 | 192.168.244.20:44641 | NULL | Sleep   | 1154 |       | NULL             |
+----+------+----------------------+------+---------+------+-------+------------------+
2 rows in set (0.03 sec)

參考

1.http://www.cnblogs.com/cenalulu/archive/2012/06/20/2554863.html

2.http://www.cnblogs.com/Alight/p/4118515.html

3.http://ronaldbradford.com/blog/sqlstatehy000-general-error-2006-mysql-server-has-gone-away-2013-01-02/