连接池超时的问题！！！

[lutaotony]

最近不知道为什么老是报数据库连接超时。
错误信息:error connecting: Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use and max pool size was reached.
根据这几天的测试估计是异步的时候导致连接没有关闭的问题。但是我检查了一些都没有发现。
public IAsyncResult IAsyncQuery(int id)
{
DataBase db = GetDataBase(DataBaseName);
using (DbConnection connection = db.CreateConnection())
{
connection.Open();
using (DbCommand command = db.GetSqlStringCommand(base["Select语句"]))
{
db.AddInParameter(command, "id", DbType.Int32, id);
return db.ExecuteAsyncDataReader(command, CommandBehavior.CloseConnection);
}
connection.Close();
}
}
恳请高手赐教。
本人新手没多少分，见谅！！

[lutaotony]

为什么我不用异步的没问题呢
public DataTable Query(int id)
{
DataBase db = GetDataBase(DataBaseName);
using (DbCommand command = db.GetSqlStringCommand(base["Select"]))
{
db.AddInParameter(command, "id", DbType.Int32, id);
return db.ExecuteDataSet(command).Tables[0];
}
}

[卧_槽]

using (DbCommand command = db.GetSqlStringCommand(base["Select语句"]))
{
db.AddInParameter(command, "id", DbType.Int32, id);
return db.ExecuteAsyncDataReader(command, CommandBehavior.CloseConnection);
}
connection.Close();
在close之前，已经return了，所以这里连接未关闭

[lutaotony]

那么应该return放在外面吗？

[lutaotony]

请问应该怎样放呢！
using (DbCommand command = db.GetSqlStringCommand(base["Select语句"]))
{
db.AddInParameter(command, "id", DbType.Int32, id);
connection.Close();
return db.ExecuteAsyncDataReader(command, CommandBehavior.CloseConnection);
}
那这样改可以吗？，为什么using没起到作用呢？