检查 JDBC 连接是否可写；使用 preferredTestQuery 或 ConnectionTester

Question

当前设置：

服务主机 (Java) 连接到 (JDBC) 主数据库 (MySQL) 并具有从属（只读）以提高可靠性

场景：

如果发生翻转，我需要将slave升级为新的master。当前 master 变为只读，新 master 提升为读写。我希望使用测试查询（对数据库执行可写查询）自动将 C3P0 连接池刷新到新的主服务器。

想法：

探索一种自动刷新 JDBC 连接池的方法，以便它们在发生翻转时连接到新的 master（当前 master 将是 RO，slave 将被提升为 RW 并且 master cname 将被更新）

当前配置

        <property name="driverClass" value="${DriverClass}" />
        <property name="jdbcUrl" value="${ReadWriteDatabaseURL}${AccountDatabaseName}${JDBCProperties}" />
        <property name="user" value="${ReadWriteDatabaseCredentials}.principal" />
        <property name="password" value="${ReadWriteDatabaseCredentials}.credential" />
        <property name="testConnectionOnCheckout" value="true"/>
        <property name="testConnectionOnCheckin" value="false" />
        <property name="preferredTestQuery" value="update existing_table set value = now() where id = 1;"/>
        <property name="maxIdleTime" value="44000"/>
        <property name="idleConnectionTestPeriod" value="30"/>
        <property name="maxStatements" value="50"/>
        <property name="minPoolSize" value="3"/>
        <property name="maxPoolSize" value="3"/>
        <property name="acquireIncrement" value="2"/>
        <property name="checkoutTimeout" value="15000"/>
        <property name="acquireRetryDelay" value="1000"/>

将 preferredTestQuery 作为select 1 from existing_table where 1 = 0 绝对可以正常工作

方法一：

在 C3P0 配置或休眠配置中 - 使用 preferredTestQuery 作为可写查询（类似于插入/更新现有表）并在每次连接签出时执行查询（testConnectionCheckout = true）。 不确定这是否应该是一个简单的查询来测试 db 是否已启动，因为

• 插入/更新查询不起作用。可能我们需要begin, commit transaction 吗？
  • 错误：org.hibernate.engine.jdbc.spi.SqlExceptionHelper: An attempt by a client to checkout a Connection has timed out.
• 多个查询不起作用。类似create table if not exists; insert into .. ; drop table ..;
  • 错误：org.hibernate.engine.jdbc.spi.SqlExceptionHelper: An attempt by a client to checkout a Connection has timed out.

方法 2： https://www.mchange.com/projects/c3p0/#configuring_connection_testing 指的是 高级用户可以定义他们希望的任何类型的连接测试，方法是实现 ConnectionTester 并提供类的完全限定名称作为 connectionTesterClassName。 我不知道怎么做，也不知道怎么做如果它适用于可写调用

上述错误的堆栈跟踪：

Caused by: org.hibernate.exception.GenericJDBCException: Could not open connection
    at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:54) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:221) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:157) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.internal.SessionImpl.connection(SessionImpl.java:550) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.springframework.orm.hibernate4.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:450) ~[spring-orm-4.3.20.RELEASE.jar:4.3.20.RELEASE]
    ... 42 more
Caused by: java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118) ~[mchange-commons-java-0.2.10.jar:0.2.10]
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:77) ~[mchange-commons-java-0.2.10.jar:0.2.10]
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:690) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource.getConnection(AbstractRoutingDataSource.java:164) ~[spring-jdbc-4.3.20.RELEASE.jar:4.3.20.RELEASE]
    at org.hibernate.service.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:141) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:292) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:214) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:157) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.internal.SessionImpl.connection(SessionImpl.java:550) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.springframework.orm.hibernate4.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:450) ~[spring-orm-4.3.20.RELEASE.jar:4.3.20.RELEASE]
    ... 42 more
Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@4c86da0c -- timeout at awaitAvailable()
    at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1467) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:644) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:554) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:758) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:685) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140) ~[c3p0-0.9.5.1.jar:0.9.5.1]
    at org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource.getConnection(AbstractRoutingDataSource.java:164) ~[spring-jdbc-4.3.20.RELEASE.jar:4.3.20.RELEASE]
    at org.hibernate.service.jdbc.connections.internal.DatasourceConnectionProviderImpl.getConnection(DatasourceConnectionProviderImpl.java:141) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.internal.AbstractSessionImpl$NonContextualJdbcConnectionAccess.obtainConnection(AbstractSessionImpl.java:292) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.obtainConnection(LogicalConnectionImpl.java:214) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.engine.jdbc.internal.LogicalConnectionImpl.getConnection(LogicalConnectionImpl.java:157) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.hibernate.internal.SessionImpl.connection(SessionImpl.java:550) ~[hibernate-core-4.2.2.Final.jar:4.2.2.Final]
    at org.springframework.orm.hibernate4.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:450) ~[spring-orm-4.3.20.RELEASE.jar:4.3.20.RELEASE]
    ... 42 more

谢谢

Answer 1

我无法对更大的故障转移问题发表评论，但您当然可以定义一个ConnectionTester，它基本上可以满足您的任何需求。 有关简明说明，请参阅apidocs for the UnifiedConnectionTester interface。

c3p0 的内置 ConnectionTester 使用 Statement.executeQuery(...)，因此 INSERTs 等可能无法正常工作。您的自定义 ConnectionTester 可以为所欲为。如果将preferredTestQuery 和rootCauseOutParamHolder 设置为null（在任何一种方法中），您应该确定它会做一些合理的事情。

如果您希望可以忽略preferredTestQuery，或者要求它为空（即，如果设置了preferredTestQuery，则抛出Exception）。