java - 如何以编程方式确定连接池大小？

Question

有没有办法以编程方式确定数据库连接池大小(已使用的连接/连接池中剩余的连接)？我们将 Hibernate 与 C3P0 结合使用。

我们在连接到数据库时遇到问题。抛出以下异常，数据未保存在数据库中。

1005,MA,19/09/11 09:39:14,com.novosys.gtw.business.frontend.SnapshotMessageBusiness.save, Major: Cannot open connection
org.hibernate.exception.GenericJDBCException: Cannot open connection
    at org.hibernate.exception.SQLStateConverter.handledNonSpecificException(SQLStateConverter.java:126)
    at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:114)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:66)
    at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:52)
    at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:449)
    at org.hibernate.jdbc.ConnectionManager.getConnection(ConnectionManager.java:167)
    at org.hibernate.jdbc.JDBCContext.connection(JDBCContext.java:142)
    at org.hibernate.transaction.JDBCTransaction.begin(JDBCTransaction.java:85)
    at org.hibernate.impl.SessionImpl.beginTransaction(SessionImpl.java:1354)
    at sun.reflect.GeneratedMethodAccessor6.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:585)
    at org.hibernate.context.ThreadLocalSessionContext$TransactionProtectionWrapper.invoke(ThreadLocalSessionContext.java:342)
    at $Proxy0.beginTransaction(Unknown Source)
    at com.novosys.gtw.util.base.BaseBusiness.save(BaseBusiness.java:199)
    at com.novosys.gtw.business.backend.receivesnapshotmessage.filter.SaveMessageFilter.decode(SaveMessageFilter.java:102)
    at org.apache.mina.filter.codec.demux.DemuxingProtocolCodecFactory$ProtocolDecoderImpl.doDecode(DemuxingProtocolCodecFactory.java:292)
    at org.apache.mina.filter.codec.CumulativeProtocolDecoder.decode(CumulativeProtocolDecoder.java:133)
    at org.apache.mina.filter.codec.ProtocolCodecFilter.messageReceived(ProtocolCodecFilter.java:158)
    at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
    at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
    at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
    at com.novosys.gtw.business.backend.receivesnapshotmessage.filter.WhitelistFilter.messageReceived(WhitelistFilter.java:231)
    at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
    at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
    at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
    at com.novosys.gtw.business.backend.receivesnapshotmessage.filter.MoniterFilter.messageReceived(MoniterFilter.java:92)
    at org.apache.mina.common.support.AbstractIoFilterChain.callNextMessageReceived(AbstractIoFilterChain.java:299)
    at org.apache.mina.common.support.AbstractIoFilterChain.access$1100(AbstractIoFilterChain.java:53)
    at org.apache.mina.common.support.AbstractIoFilterChain$EntryImpl$1.messageReceived(AbstractIoFilterChain.java:648)
    at org.apache.mina.filter.executor.ExecutorFilter.processEvent(ExecutorFilter.java:220)
    at org.apache.mina.filter.executor.ExecutorFilter$ProcessEventsRunnable.run(ExecutorFilter.java:264)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
    at org.apache.mina.util.NamePreservingRunnable.run(NamePreservingRunnable.java:51)
    at java.lang.Thread.run(Thread.java:595)
Caused by: java.sql.SQLException: Connections could not be acquired from the underlying database!
    at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:106)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:529)
    at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:128)
    at org.hibernate.connection.C3P0ConnectionProvider.getConnection(C3P0ConnectionProvider.java:78)
    at org.hibernate.jdbc.ConnectionManager.openConnection(ConnectionManager.java:446)
    ... 31 more
Caused by: com.mchange.v2.resourcepool.CannotAcquireResourceException: A ResourcePool could not acquire a resource from its primary factory or source.
    at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1319)
    at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:557)
    at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:477)
    at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:525)
    ... 34 more

We tried to resolve it by increasing connection pool size and also increasing no. of connections available at MySQL level, but of no use. We are now trying to sort of debug it to see if its due to connection pool size or due to MySQL connection size. We want to log no. of connection available/in use in connection pool size but could not get any help from google.

Environment: Java, Hibernate, C3P0, MySQL

Session session = null;
Transaction transaction = null;

try {
            session = HibernateUtil.getSessionFactory(datasource).getCurrentSession();
            transaction = session.beginTransaction();
            // db save called here
            session.getTransaction().commit();
        } catch (Exception e) {
            Logger.write(LoggerConstant.MAJOR_ERROR, e.getMessage(), e, methodName);
        } finally {
            try {
                if ((transaction != null) && (transaction.isActive())) {
                    transaction.rollback();
                }
            } catch (Exception e) {
                Logger.write(LoggerConstant.CRITICAL_ERROR, e.getMessage(), e, methodName);
            }
            try {
                if ((session != null) && (session.isOpen())) {
                    session.close();
                }
            } catch (Exception e) {
                Logger.write(LoggerConstant.CRITICAL_ERROR, e.getMessage(), e, methodName);
            }
        }

Answer 1

我不认为您的问题是连接池本身，而是更普遍的连接泄漏。此问题通常与 HibernateDaoSupport.getSession() 的使用没有与 HibernateDaoSupport.releaseSession() 正确配对有关。一般来说，你想要类似的东西

public SomeObject getSomething() 
{ 
    Session session = null;
    try 
    {
        session = this.getSession();
        Query query = session.createSQLQuery("SELECT * FROM SomeTable WHERE SomeClause").addEntity(SomeObject.class); 

        // extract object from query 

        return someObject; 
    } 
    finally 
    {
        if (session != null) 
            this.releaseSession(session);
    }        
}

这可以通过使用 HibernateCallback 自动完成。您可以通过向 this.getHibernateTemplate().executeFind 提供查询来执行此操作，这将在 Hibernate 中使用具有自动资源管理的 session 。