的PostgreSQL +休眠+ C3P0 = FATAL：對不起，太多的客戶已經

Question

我有以下代碼

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> 

後幾秒鐘和一些成功的插入，以下除外離子出現：

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) 

看起來，休眠並沒有實現連接。但hibernateSession.close()會導致異常Session is closed，因爲調用了tx.commit()。

Answer 1

我發現原因爲什麼c3p0表現這種方式。這個問題是相當微不足道的...... 此部分代碼：

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

已執行多次。謝謝史蒂夫的提示。

Answer 2

我建議你使用try-catch-finally塊，

在 finally

親切關閉會話

即

try {   
     tx.commit(); 
    } catch (HibernateException e) { 
     handleException(e); 
    } finally { 
     hibernateSession.close(); 
    } 

而且，
postgresql.conf裏面的max_connections財產是100默認。如果你需要的話增加它。

Answer 3

我不太確定這裏發生了什麼事，但我建議你不要將hibernate.c3p0.acquireRetryAttempts設置爲1.首先，呈現下一個設置hibernate.c3p0.acquireRetryDelay不相關 - 設置重試嘗試之間的時間長度，但如果只有一次嘗試（確定，參數名稱具有誤導性，它會設置嘗試的總次數），則不會重試。您的設置的效果僅僅是讓客戶端在客戶端進入時嘗試獲取連接，然後在客戶端出現故障時立即向客戶端拋出異常。它完全不會限制池將嘗試獲取的連接數量（除非您將breakOnAcquireFailure設置爲true，在這種情況下，使用您的設置，任何未能獲取連接將導致整個池無效）。

我分享了sola對您缺乏可靠資源清理的擔憂。如果在你的設置下，commit（）意味着close（）（你不允許顯式地調用close（這看起來很糟糕）），那麼它應該是在finally塊中的提交（但是在finally塊中提交也看起來很糟糕，有時你不想提交）。無論關閉/提交問題，使用您擁有的代碼，偶爾在openSession和commit之間發生異常都會導致Connection泄漏。

但是，這不應該是你的太多開放連接問題的原因。如果泄漏Connections，您會發現連接池最終會凍結（因爲泄漏導致maxPoolSize Connectiosn將永久簽出）。你只有25個開放的連接。其他事情正在發生。嘗試查看您的日誌。多個連接池以某種方式被初始化？ （c3p0在pool init的INFO級別上轉儲配置信息，因此如果打開多個池，應該會看到多條消息。或者，您可以通過JMX檢查運行的c3p0池，以查看是否爲什麼打開了超過25個連接。 ）

祝你好運！