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mysql5,mysql5.6,mysql5.7,mysql8设置autoReconnect=true解决连接数据库超时问m

来源:  2018-09-07 14:34:37    评论:0点击:

1,问题现象:

com.mysql.jdbc.CommunicationsException: The last packet successfully received from the server was58129 seconds ago.The last packet sent successfully to the server was 58129 seconds ago, which is longer than the server configured value of 'wait_timeout'. You should consider either expiring and/or testing connection validity before use in your application, increasing the server configured values for client timeouts, or using the Connector/J connection property 'autoReconnect=true' to avoid this problem. 

解决办法: 

(备注:mysql5以上的,设置autoReconnect=true 是有的 ,起作用)

看看官网 mysql8.0上关于 autoReconnect的设置:https://dev.mysql.com/doc/refman/8.0/en/c-api-auto-reconnect.html

he MySQL client library can perform an automatic reconnection to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. If auto-reconnect is enabled, the library tries once to reconnect to the server and send the statement again.

Auto-reconnect is disabled by default.     

看看官网 mysql5.7上关于 autoReconnect的设置:
 

27.8.20 C API Automatic Reconnection Control

 

The MySQL client library can perform an automatic reconnection to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. If auto-reconnect is enabled, the library tries once to reconnect to the server and send the statement again.

Auto-reconnect is disabled by default.

If it is important for your application to know that the connection has been dropped (so that it can exit or take action to adjust for the loss of state information), be sure that auto-reconnect is disabled. To ensure this, call mysql_options() with the MYSQL_OPT_RECONNECT option:     


看看官网 mysql5.6上关于 autoReconnect的设置:

 

       The MySQL client library can perform an automatic reconnection to the server if it finds that the connection is down when you attempt to send a statement to the server to be executed. If auto-reconnect is enabled, the library tries once to reconnect to the server and send the statement again.

Auto-reconnect is disabled by default.

If it is important for your application to know that the connection has been dropped (so that it can exit or take action to adjust for the loss of state information), be sure that auto-reconnect is disabled. To ensure this, call mysql_options() with the MYSQL_OPT_RECONNECT option:     

如果连接闲置8小时 (8小时内没有进行数据库操作), mysql就会自动断开连接, 要重启tomcat. 
    不用hibernate的话, connection url加参数: autoReconnect=true 
    用hibernate的话, 加如下属性: 
        <property name="connection.autoReconnect">true</property> 
        <property name="connection.autoReconnectForPools">true</property> 
        <property name="connection.is-connection-validation-required">true</property>
 
    要是还用c3p0连接池: 
        <property name="hibernate.c3p0.acquire_increment">1</property> 
        <property name="hibernate.c3p0.idle_test_period">0</property> 
        <property name="hibernate.c3p0.timeout">0</property> 
        <property name="hibernate.c3p0.validate">true</property>

 以上转载链接地址:http://blog.aqsc.cn/article.php?type=blog&itemid=1016

2,另外:关于Mysql链接参数的说明如下:

 

mysql JDBC Driver

常用的有两个,一个是gjt(Giant Java Tree)组织提供的mysql驱动,其JDBC Driver名称(JAVA类名)为:org.gjt.mm.mysql.Driver

详情请参见网站:http://www.gjt.org/

或在本网站下载mysql JDBC Driver(mm.jar)

另一个是mysql官方提供的JDBC Driver,其JAVA类名为:com.mysql.jdbc.Driver

驱动下载网址:http://dev.mysql.com/downloads/,进入其中的MySQL Connector/J区域下载。

mysql JDBC URL格式如下:

jdbc:mysql://[host:port],[host:port].../[database][?参数名1][=参数值1][&参数名2][=参数值2]...

现只列举几个重要的参数,如下表所示:

参数名称 参数说明 缺省值 最低版本要求
user 数据库用户名(用于连接数据库)   所有版本
password 用户密码(用于连接数据库)   所有版本
useUnicode 是否使用Unicode字符集,如果参数characterEncoding设置为gb2312或gbk,本参数值必须设置为true false 1.1g
characterEncoding 当useUnicode设置为true时,指定字符编码。比如可设置为gb2312或gbk false 1.1g
autoReconnect 当数据库连接异常中断时,是否自动重新连接? false 1.1
autoReconnectForPools 是否使用针对数据库连接池的重连策略 false 3.1.3
failOverReadOnly 自动重连成功后,连接是否设置为只读? true 3.0.12
maxReconnects autoReconnect设置为true时,重试连接的次数 3 1.1
initialTimeout autoReconnect设置为true时,两次重连之间的时间间隔,单位:秒 2 1.1
connectTimeout 和数据库服务器建立socket连接时的超时,单位:毫秒。 0表示永不超时,适用于JDK 1.4及更高版本 0 3.0.1
socketTimeout socket操作(读写)超时,单位:毫秒。 0表示永不超时 0 3.0.1

 

对应中文环境,通常mysql连接URL可以设置为:

jdbc:mysql://localhost:3306/test?user=root&password=&useUnicode=true&characterEncoding=gbk&autoReconnect=true&failOverReadOnly=false

在使用数据库连接池的情况下,最好设置如下两个参数:

autoReconnect=true&failOverReadOnly=false

需要注意的是,在xml配置文件中,url中的&符号需要转义成&。比如在tomcat的server.xml中配置数据库连接池时,mysql jdbc url样例如下:

jdbc:mysql://localhost:3306/test?user=root&amp;password=&amp;useUnicode=true&amp;characterEncoding=gbk

&amp;autoReconnect=true&amp;failOverReadOnly=false

其他参数请参见mysql jdbc官方文档: MySQL Connector/J Documentation

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