我有一个应用程序，使用hibernate（v3.6.4），连接池由C3P0（v0.9.1.2）提供。
问题是，如果我进行了数据库查询，并且该应用程序进程（因此也是C3P0池）运行的时间超过MySQL wait_timeout值，我会遇到JDBC通信链路故障。为了测试这个问题，我在/etc/mysql/my.cnf中将wait_timeout的值设置为600秒。
这似乎是一个普遍的问题，为了解决这个问题，我尝试了调整这些Hibernate / c3p0属性，并检查了Hibernate / c3p0文档和在Stack Overflow上已经提出的问题的答案：
相关的Hibernate属性：
从上述日志中，我们可以看到C3P0的testConnectionOnCheckout=true和autoReconnect=true。有没有人能帮我弄清楚为什么C3P0会检出一个超时的连接呢？谢谢。
问题是，如果我进行了数据库查询，并且该应用程序进程（因此也是C3P0池）运行的时间超过MySQL wait_timeout值，我会遇到JDBC通信链路故障。为了测试这个问题，我在/etc/mysql/my.cnf中将wait_timeout的值设置为600秒。
2013-01-27 20:08:00,088 ERROR [Thread-0] (JDBCExceptionReporter.java:234) - Communications link failure
The last packet successfully received from the server was 665,943 milliseconds ago. The last packet sent successfully to the server was 6 milliseconds ago.
org.hibernate.exception.JDBCConnectionException: could not execute query
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:99)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
at org.hibernate.loader.Loader.doList(Loader.java:2536)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
.....
Caused by: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure
The last packet successfully received from the server was 665,943 milliseconds ago. The last packet sent successfully to the server was 6 milliseconds 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:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3102)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:2991)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3532)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxyPreparedStatement.java:76)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
at org.hibernate.loader.Loader.doQuery(Loader.java:802)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2533)
... 9 more
Caused by: java.io.EOFException: Can not read response from server. Expected to read 4 bytes, read 0 bytes before connection was unexpectedly lost.
at com.mysql.jdbc.MysqlIO.readFully(MysqlIO.java:2552)
at com.mysql.jdbc.MysqlIO.reuseAndReadPacket(MysqlIO.java:3002)
... 22 more
2013-01-27 20:19:00,179 WARN [Thread-0] (NewPooledConnection.java:487) - [c3p0] Another error has occurred [ com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 1,326,037 milliseconds ago. The last packet sent successfully to the server was 660,100 milliseconds ago. 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. ] which will not be reported to listeners!
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: The last packet successfully received from the server was 1,326,037 milliseconds ago. The last packet sent successfully to the server was 660,100 milliseconds ago. 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.
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:411)
at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1116)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3364)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1983)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeQuery(PreparedStatement.java:2293)
at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeQuery(NewProxyPreparedStatement.java:76)
at org.hibernate.jdbc.AbstractBatcher.getResultSet(AbstractBatcher.java:208)
at org.hibernate.loader.Loader.getResultSet(Loader.java:1953)
at org.hibernate.loader.Loader.doQuery(Loader.java:802)
at org.hibernate.loader.Loader.doQueryAndInitializeNonLazyCollections(Loader.java:274)
at org.hibernate.loader.Loader.doList(Loader.java:2533)
at org.hibernate.loader.Loader.listIgnoreQueryCache(Loader.java:2276)
at org.hibernate.loader.Loader.list(Loader.java:2271)
at org.hibernate.loader.criteria.CriteriaLoader.list(CriteriaLoader.java:119)
at org.hibernate.impl.SessionImpl.list(SessionImpl.java:1716)
at org.hibernate.impl.CriteriaImpl.list(CriteriaImpl.java:347)
....
Caused by: java.net.SocketException: Broken pipe
at java.net.SocketOutputStream.socketWrite0(Native Method)
at java.net.SocketOutputStream.socketWrite(Unknown Source)
at java.net.SocketOutputStream.write(Unknown Source)
at java.io.BufferedOutputStream.flushBuffer(Unknown Source)
at java.io.BufferedOutputStream.flush(Unknown Source)
at com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3345)
... 20 more
这似乎是一个普遍的问题，为了解决这个问题，我尝试了调整这些Hibernate / c3p0属性，并检查了Hibernate / c3p0文档和在Stack Overflow上已经提出的问题的答案：
相关的Hibernate属性：
<property name="hibernate.connection.driver_class">com.mysql.jdbc.Driver</property>
<property name="hibernate.connection.url">jdbc:mysql://localhost:3306/gsui?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true</property>
<property name="hibernate.connection.autoReconnect">true</property>
<!-- C3p0 Performance Improvements -->
<property name="hibernate.c3p0.acquire_increment">1</property>
<property name="hibernate.c3p0.idle_test_period">300</property>
<property name="hibernate.c3p0.maxConnectionAge">3600</property>
<property name="hibernate.c3p0.timeout">120</property>
<property name="hibernate.c3p0.max_size">300</property>
<property name="hibernate.c3p0.min_size">1</property>
<property name="hibernate.c3p0.max_statements">100</property>
<property name="hibernate.c3p0.preferredTestQuery">select 1;</property>
<property name="hibernate.connection.useUnicode">
true
</property>
<property name="hibernate.connection.characterEncoding">
UTF-8
</property>
<property name="hibernate.connection.charSet">
UTF-8
</property>
我还在我维护的c3p0属性文件中将c3p0.testConnectionOnCheckout设置为true：
c3p0.testConnectionOnCheckout=true
在日志中，C3P0池使用以下信息正常初始化：
2013-01-27 19:45:04,607 INFO [main] (ConnectionProviderFactory.java:173) - Initializing connection provider: org.hibernate.connection.C3P0ConnectionProvider
2013-01-27 19:45:04,609 INFO [main] (C3P0ConnectionProvider.java:103) - C3P0 using driver: com.mysql.jdbc.Driver at URL: jdbc:mysql://localhost:3306/gsui?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true
2013-01-27 19:45:04,610 INFO [main] (C3P0ConnectionProvider.java:104) - Connection properties: {useUnicode=true, autoReconnect=true, user=root, password=****, shutdown=true, characterEncoding=UTF-8, charSet=UTF-8}
2013-01-27 19:45:04,610 INFO [main] (C3P0ConnectionProvider.java:107) - autocommit mode: false
2013-01-27 19:45:04,629 INFO [main] (MLog.java:80) - MLog clients using log4j logging.
2013-01-27 19:45:04,757 INFO [main] (C3P0Registry.java:204) - Initializing c3p0-0.9.1.2 [built 21-May-2007 15:04:56; debug? true; trace: 10]
2013-01-27 19:45:04,842 INFO [main] (C3P0ConnectionProvider.java:194) - JDBC isolation level: READ_COMMITTED
2013-01-27 19:45:04,871 INFO [main] (AbstractPoolBackedDataSource.java:462) - Initializing c3p0 pool... com.mchange.v2.c3p0.PoolBackedDataSource@9f4a7137 [ connectionPoolDataSource -> com.mchange.v2.c3p0.WrapperConnectionPoolDataSource@71b9e1e9 [ acquireIncrement -> 1, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, debugUnreturnedConnectionStackTraces -> false, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> z8kfsx8sz4pted1s4b69w|51f726b9, idleConnectionTestPeriod -> 300, initialPoolSize -> 1, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 3600, maxIdleTime -> 120, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 300, maxStatements -> 100, maxStatementsPerConnection -> 0, minPoolSize -> 1, nestedDataSource -> com.mchange.v2.c3p0.DriverManagerDataSource@58f45048 [ description -> null, driverClass -> null, factoryClassLocation -> null, identityToken -> z8kfsx8sz4pted1s4b69w|454b7177, jdbcUrl -> jdbc:mysql://localhost:3306/gsui?useUnicode=true&characterEncoding=UTF-8&autoReconnect=true, properties -> {useUnicode=true, autoReconnect=true, user=******, password=******, shutdown=true, characterEncoding=UTF-8, charSet=UTF-8} ], preferredTestQuery -> select 1;, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> true, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false; userOverrides: {} ], dataSourceName -> null, factoryClassLocation -> null, identityToken -> z8kfsx8sz4pted1s4b69w|71ffd9f1, numHelperThreads -> 3 ]
从上述日志中，我们可以看到C3P0的testConnectionOnCheckout=true和autoReconnect=true。有没有人能帮我弄清楚为什么C3P0会检出一个超时的连接呢？谢谢。