请教关于大数据量高频率批量插入数据库操作时数据库连接池连接使用问题

我们的系统是做信息数据采集的，将所有采集的数据存库，但是数据量是非常大的一天能够达到上千万的数据入库，在处理的过程中数据库连接使用过程中经常会出现一些问题，我使用的是C3P0的连接池，连接数给到20个用到一段时间后大概在几个小时就会出现如下异常信息
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.c3p0.impl.NewPooledConnection -com.mchange.v2.c3p0.impl.NewPooledConnection@b4e29 b closed by a client.
java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE
at com.mchange.v2.c3p0.impl.NewPooledConnection.close (NewPooledConnection.java:491)
at com.mchange.v2.c3p0.impl.NewPooledConnection.close (NewPooledConnection.java:191)
at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool$ 1PooledConnectionResourcePoolManager.destroyResour ce(C3P0PooledConnectionPool.java:470)
at com.mchange.v2.resourcepool.BasicResourcePool$1Des troyResourceTask.run(BasicResourcePool.java:964)
at com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread.run(ThreadPoolAsynchronousRunner.java:5 47)
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool -Successfully destroyed PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@b4e29 b
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.resourcepool.BasicResourcePool -Successfully destroyed resource: com.mchange.v2.c3p0.impl.NewPooledConnection@b4e29 b
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.resourcepool.BasicResourcePool -Preparing to destroy resource: com.mchange.v2.c3p0.impl.NewPooledConnection@50988
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool -Preparing to destroy PooledConnection: com.mchange.v2.c3p0.impl.NewPooledConnection@50988
18/12/2007 11:56:44 [com.mchange.v2.async.ThreadPoolAsynchronousRunner$ PoolThread-#2] com.mchange.v2.c3p0.impl.NewPooledConnection -com.mchange.v2.c3p0.impl.NewPooledConnection@50988 closed by a client.
java.lang.Exception: DEBUG -- CLOSE BY CLIENT STACK TRACE




出现上面的异常信息后我的连接数由20个变成了5个，上网查了也没有什么具体的说法请教各位知道不知道这个问题的原因是什么。我用的数据库是DB2 9.7