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我的代码是用 jRuby 编写的，我使用 Warbler 部署在 Tomcat 中。我正在使用 Sequel 来查询 MySQL 数据库。我正在使用两层数据库连接池。一种是原生 Sequel 池，另一种是 Tomcat 级别的 JNDI 池。连接字符串是：

DB = Sequel.connect("jdbc:jndi:java:comp/env/test", :logger => $db_log, :max_connections => 10)

此连接字符串在 app.rb 中定义，仅在有新部署或重新启动 Tomcat 时才会加载。这将创建一个 Sequel 连接池，并且所有线程共享该池。我的 JNDI 配置$CATALINA_OME/conf/context.xml是：

<Resource
name="test"
auth="Container"
type="javax.sql.DataSource"
maxActive="10"
maxIdle="5"
maxWait="9000"
username="test_db"
password="test_db"
driverClassName="com.mysql.jdbc.Driver"
testOnBorrow="true"
testWhileIdle="true"
validationQuery="SELECT 1" testOnReturn="true"
timeBetweenEvictionRunsMillis="300000" removeAbandonedTimeout="60"
removeAbandoned="true"
logAbandoned="true"
url="jdbc:mysql://IP:3306/test"
/>

我DB.disconnect用于将连接返回到 JNDI 池，以确保没有线程使用以前使用过的连接。我这样做是为了确保wait_timeout错误。auto_reconnect=true似乎无法wait_timeout正确解决问题。一切正常，直到几天前我开始遇到以下错误：

W, [2012-07-26T05:10:30.999000 #29456]  WARN -- : 134325951259087 == NativeException: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
D, [2012-07-26T05:10:31.001000 #29456] DEBUG -- : 134325951259087 == ["sun.reflect.GeneratedConstructorAccessor23:-1:in `newInstance'", "sun/reflect/DelegatingConstructorAccessorImpl.java:27:in `newInstance'", "java/lang/reflect/Constructor.java:513:in `newInstance'", "com/mysql/jdbc/Util.java:409:in `handleNewInstance'", "com/mysql/jdbc/SQLError.java:1118:in `createCommunicationsException'", "com/mysql/jdbc/MysqlIO.java:343:in `<init>'", "com/mysql/jdbc/ConnectionImpl.java:2308:in `connectOneTryOnly'", "com/mysql/jdbc/ConnectionImpl.java:2122:in `createNewIO'", "com/mysql/jdbc/ConnectionImpl.java:774:in `<init>'", "com/mysql/jdbc/JDBC4Connection.java:49:in `<init>'", "sun.reflect.GeneratedConstructorAccessor25:-1:in `newInstance'", "sun/reflect/DelegatingConstructorAccessorImpl.java:27:in `newInstance'", "java/lang/reflect/Constructor.java:513:in `newInstance'", "com/mysql/jdbc/Util.java:409:in `handleNewInstance'"

和

W, [2012-07-26T10:19:14.029000 #1572]  WARN -- : 134327815053548 == NativeException: java.sql.SQLException: Connection com.mysql.jdbc.JDBC4Connection@5a0655d is closed.
D, [2012-07-26T10:19:14.030000 #1572] DEBUG -- : 134327815053548 == ["org/apache/tomcat/dbcp/dbcp/DelegatingConnection.java:398:in `checkOpen'", "org/apache/tomcat/dbcp/dbcp/DelegatingConnection.java:255:in `createStatement'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/adapters/jdbc.rb:523:in `statement'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/adapters/jdbc.rb:233:in `execute'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/connection_pool/threaded.rb:88:in `hold'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/database/connecting.rb:234:in `synchronize'", "file:/usr/local/tomcat-instance/testv/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/adapters/jdbc.rb:232:in `execute'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/lib/santa-gems.jar!/gems/sequel-3.34.0/lib/sequel/dataset/actions.rb:744:in `execute'", "file:/usr/local/tomcat-instance/test/webapps/service/WEB-INF/l

这些错误发生得太频繁，不容忽视。

唯一发生的变化是数据库主机，但我确保超时变量保持不变。这些值为：

interactive_timeout=300
connect_timeout=300
wait_timeout=10

还有什么可以产生差异的吗？

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1 回答 1

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“通信链接失败”通常意味着您的程序根本无法连接到数据库。典型的问题是不正确的主机名和端口号（很容易再次检查）或者在您的程序和数据库之间存在一个或多个防火墙，包括软件和硬件。

最好（如果可以的话）使用命令行mysql实用程序来验证您是否可以从运行应用程序的机器连接到数据库服务器。如果可行，那么您需要检查您的<Resource>配置。如果它不起作用，那么您将需要查看防火墙的存在。

请注意，最新版本的 Microsoft Windows（例如）默认启用防火墙，这可能不允许您的程序通过无法识别的端口 (3306) 进行外部连接。因此，首先检查您的本地（即在运行 webapp 的机器上）防火墙配置，然后与您的网络管理员联系，看看是否有其他防火墙挡住了路，如果事情不工作。

于 2012-07-26T16:58:07.620 回答