Question

我有以下代码

    Configuration config = new Configuration().configure();
    config.buildMappings();
    serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 
    SessionFactory factory = config.buildSessionFactory(serviceRegistry);
    Session hibernateSession = factory.openSession();
    Transaction tx = hibernateSession.beginTransaction();
    ObjectType ot = (ObjectType)hibernateSession.merge(someObj);
    tx.commit();
    return ot;

hibernate.cfg.xml包含：

<session-factory>

    <property name="connection.url">jdbc:postgresql://127.0.0.1:5432/dbase</property>
    <property name="hibernate.dialect">org.hibernate.dialect.PostgreSQLDialect</property>
    <property name="connection.driver_class">org.postgresql.Driver</property>

    <property name="connection.username">username</property>
    <property name="connection.password">password</property>

    <property name="connection.provider_class">org.hibernate.connection.C3P0ConnectionProvider</property>        
    <property name="hibernate.c3p0.acquire_increment">1</property>
    <property name="hibernate.c3p0.min_size">5</property>
    <property name="hibernate.c3p0.max_size">20</property>
    <property name="hibernate.c3p0.max_statements">50</property>
    <property name="hibernate.c3p0.timeout">300</property>
    <property name="hibernate.c3p0.idle_test_period">3000</property>
    <property name="hibernate.c3p0.acquireRetryAttempts">1</property>
    <property name="hibernate.c3p0.acquireRetryDelay">250</property>

    <property name="hibernate.show_sql">true</property>
    <property name="hibernate.use_sql_comments">true</property>

    <property name="hibernate.transaction.factory_class">org.hibernate.transaction.JDBCTransactionFactory</property>
    <property name="hibernate.current_session_context_class">thread</property>

    <mapping class="...." />

</session-factory>

几秒钟后，一些成功的插入会出现以下异常：

org.postgresql.util.PSQLException: FATAL: sorry, too many clients already
    at org.postgresql.core.v3.ConnectionFactoryImpl.doAuthentication(ConnectionFactoryImpl.java:291)
    at org.postgresql.core.v3.ConnectionFactoryImpl.openConnectionImpl(ConnectionFactoryImpl.java:108)
    at org.postgresql.core.ConnectionFactory.openConnection(ConnectionFactory.java:66)
    at org.postgresql.jdbc2.AbstractJdbc2Connection.<init>(AbstractJdbc2Connection.java:125)
    at org.postgresql.jdbc3.AbstractJdbc3Connection.<init>(AbstractJdbc3Connection.java:30)
    at org.postgresql.jdbc3g.AbstractJdbc3gConnection.<init>(AbstractJdbc3gConnection.java:22)
    at org.postgresql.jdbc4.AbstractJdbc4Connection.<init>(AbstractJdbc4Connection.java:30)
    at org.postgresql.jdbc4.Jdbc4Connection.<init>(Jdbc4Connection.java:24)
    at org.postgresql.Driver.makeConnection(Driver.java:393)
    at org.postgresql.Driver.connect(Driver.java:267)
    at com.mchange.v2.c3p0.DriverManagerDataSource.getConnection(DriverManagerDataSource.java:135)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:182)
    at com.mchange.v2.c3p0.WrapperConnectionPoolDataSource.getPooledConnection(WrapperConnectionPoolDataSource.java:171)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$1PooledConnectionResourcePoolManager.acquireResource(C3P0PooledConnectionPool.java:137)
    at com.mchange.v2.resourcepool.BasicResourcePool.doAcquire(BasicResourcePool.java:1014)
    at com.mchange.v2.resourcepool.BasicResourcePool.access$800(BasicResourcePool.java:32)
    at com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask.run(BasicResourcePool.java:1810)
    at com.mchange.v2.async.ThreadPoolAsynchronousRunner$PoolThread.run(ThreadPoolAsynchronousRunner.java:547)
12:24:19.151 [          Thread-160] WARN                   internal.JdbcServicesImpl - HHH000342: Could not obtain connection to query metadata : Connections could not be acquired from the underlying database!
12:24:19.151 [          Thread-160] INFO                             dialect.Dialect - HHH000400: Using dialect: org.hibernate.dialect.PostgreSQLDialect
12:24:19.151 [          Thread-160] INFO                  internal.LobCreatorBuilder - HHH000422: Disabling contextual LOB creation as connection was null
12:24:19.151 [          Thread-160] INFO        internal.TransactionFactoryInitiator - HHH000268: Transaction strategy: org.hibernate.engine.transaction.internal.jdbc.JdbcTransactionFactory
12:24:19.151 [          Thread-160] INFO               ast.ASTQueryTranslatorFactory - HHH000397: Using ASTQueryTranslatorFactory
12:24:19.151 [          Thread-160] INFO                        hbm2ddl.SchemaUpdate - HHH000228: Running hbm2ddl schema update
12:24:19.151 [          Thread-160] INFO                        hbm2ddl.SchemaUpdate - HHH000102: Fetching database metadata
12:24:19.211 [Runner$PoolThread-#0] WARN              resourcepool.BasicResourcePool - com.mchange.v2.resourcepool.BasicResourcePool$AcquireTask@ee4084 -- Acquisition Attempt Failed!!! Clearing pending acquires. While trying to acquire a needed new resource, we failed to succeed more than the maximum number of allowed acquisition attempts (1). Last acquisition attempt exception: 
org.postgresql.util.PSQLException: FATAL: sorry, too many clients already
    at org.postgresql.core.v3.ConnectionFactoryImpl.doAuthentication(ConnectionFactoryImpl.java:291)

似乎hibernate没有实现连接。但hibernateSession.close()导致异常Session is closed，因为tx.commit()被调用。

Answer 1

我不太确定这里发生了什么，但我建议你不要将hibernate.c3p0.acquireRetryAttempts设置为1.首先，这会使你的下一个设置，hibernate.c3p0.acquireRetryDelay无关紧要 - 设置长度重试尝试之间的时间，但如果只有一次尝试（好的，参数名称有误导性，它设置了尝试的总次数），则没有重试。设置的效果只是让池在客户端进入时尝试获取Connection，如果失败则立即向客户端抛出异常。它根本不会限制池尝试获取的连接数（除非您将breakOnAcquireFailure设置为true，在这种情况下，使用您的设置，任何获取Connection的失败都会使整个池无效。）

我同意sola对您缺乏可靠资源清理的担忧。如果在你的设置下，commit（）意味着close（）（并且你不允许显式调用close？这看起来很糟糕），那么它应该是在finally块中的提交（但是在finally块中的提交也看起来很糟糕），有时候你不想提交）。无论close / commit的问题是什么，使用你拥有的代码，openSession和commit之间的偶然异常都会导致Connection泄漏。

但这不应该是你太多开放连接问题的原因。如果泄漏Connections，您会发现连接池最终冻结（因为泄漏导致maxPoolSize Connectiosn永远被检出）。您只有25个打开的连接。还有其他事情正在发生。尝试查看您的日志。以某种方式初始化多个连接池？（c3p0在池初始化转储INFO级别的配置信息，因此如果打开多个池，您应该看到多个消息。或者，您可以通过JMX检查正在运行的c3p0池，以查看是否/为什么打开了超过25个连接。）

祝你好运！

Answer 2

我找到了c3p0以这种方式表现的原因。这个问题非常简单...... 这部分代码：

Configuration config = new Configuration().configure();
config.buildMappings();
serviceRegistry = new ServiceRegistryBuilder().applySettings(config.getProperties()).buildServiceRegistry(); 
SessionFactory factory = config.buildSessionFactory(serviceRegistry);

被执行了多次。谢谢史蒂夫的小费。

Answer 3

我建议你使用 try-catch-finally 阻止，

<{1>}中的

请关闭会话

即

 finally

还有，
postgresql.conf中的try { tx.commit(); } catch (HibernateException e) { handleException(e); } finally { hibernateSession.close(); }属性默认为100。如果需要，可以增加它。

PostgreSQL + Hibernate + C3P0 =致命：抱歉，已经有太多客户了

3 个答案: