I am closing this issue as it did not have any updates since 2012. Please feel free to reopen it if you think it is still relevant.

Any update on this one? I am getting the exact same exception with Hibernate 3.3.1.GA, Oracle with ojdbc5-11.2.0.3:

java.sql.SQLException: IO Error: Socket closed
at oracle.jdbc.driver.T4CConnection.logoff(T4CConnection.java:556)
at oracle.jdbc.driver.PhysicalConnection.close(PhysicalConnection.java:3968)
at org.hibernate.connection.DriverManagerConnectionProvider.close(DriverManagerConnectionProvider.java:175)
at org.hibernate.connection.DriverManagerConnectionProvider.finalize(DriverManagerConnectionProvider.java:165)
at java.lang.ref.Finalizer.invokeFinalizeMethod(Native Method)
at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:83)
at java.lang.ref.Finalizer.access$100(Finalizer.java:14)
at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:160)
Caused by: java.net.SocketException: Socket closed
at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:99)
at java.net.SocketOutputStream.write(SocketOutputStream.java:136)
at oracle.net.ns.DataPacket.send(DataPacket.java:210)
at oracle.net.ns.NetOutputStream.flush(NetOutputStream.java:230)
at oracle.net.ns.NetInputStream.getNextPacket(NetInputStream.java:312)
at oracle.net.ns.NetInputStream.read(NetInputStream.java:260)
at oracle.net.ns.NetInputStream.read(NetInputStream.java:185)
at oracle.net.ns.NetInputStream.read(NetInputStream.java:102)
at oracle.jdbc.driver.T4CSocketInputStreamWrapper.readNextPacket(T4CSocketInputStreamWrapper.java:124)
at oracle.jdbc.driver.T4CSocketInputStreamWrapper.read(T4CSocketInputStreamWrapper.java:80)
at oracle.jdbc.driver.T4CMAREngine.unmarshalUB1(T4CMAREngine.java:1137)
at oracle.jdbc.driver.T4CTTIfun.receive(T4CTTIfun.java:290)
at oracle.jdbc.driver.T4CTTIfun.doRPC(T4CTTIfun.java:192)
at oracle.jdbc.driver.T4C7Ocommoncall.doOLOGOFF(T4C7Ocommoncall.java:61)
at oracle.jdbc.driver.T4CConnection.logoff(T4CConnection.java:543)
... 7 more

Oracle DB server and Oracle JDBC Driver version mismatch could cause Socket Closed exception.

I'm also getting the same error.

2007-08-24 11:28:27,165 WARN [org.hibernate.connection.DriverManagerConnectionProvider] problem closing pooled connection
java.sql.SQLException: Io exception: Socket closed
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:158)

If i add the cache configuration. working fine for me. if i use default /remove the cache configuration from hibernate.cfg.xml, we're getting this error

<property name="c3p0.acquire_increment">1</property>
<property name="c3p0.idle_test_period">100</property>
<property name="c3p0.max_size">10</property>
<property name="c3p0.max_statements">10</property>
<property name="c3p0.min_size">10</property>
<property name="c3p0.timeout">100</property>
<property name="hbm2ddl.auto">update</property>
<property name="show_sql">true</property>
<property name="hibernate.cache.provider_class">
org.hibernate.cache.OSCacheProvider
</property>
<property name="hibernate.cache.use_second_level_cache">
true
</property>