调试易

    小弟前段试着利用Bytea类型存取大对象，但是程序编好后测试发现虽然一个butea的属性可以存储高达1GB的二进制数据，但是它需要占用大量内存来完成这个大数据，实际中远达不到1G，上传一个大于13M的文件就会出现out of memory 或者connection is broken的异常，相当郁闷。当然也有可能是我程序的原因。
    现在正在初试用oid这个类型来存取，修改程序后运行，却老出现invalid large-object descriptor: 0的异常，相当的郁闷闷！希望懂这方面的好心高手帮帮小弟，先谢谢您的大恩啦！QQ一直在线：254380172
    private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog ofd = new OpenFileDialog();
            if (ofd.ShowDialog() == DialogResult.OK)
            fullfilename = ofd.FileName.ToString();
            filename = Path.GetFileName(fullfilename);
            NpgsqlConnection conn = new NpgsqlConnection("server=127.0.0.1;database=mydb;uid=postgres;pwd=1234");
            conn.Open();
            NpgsqlTransaction transaction = conn.BeginTransaction();
            LargeObjectManager lom = new LargeObjectManager(conn);
            conn.Open();
            int noid = lom.Create(LargeObjectManager.READWRITE);
            LargeObject lo = lom.Open(noid, LargeObjectManager.WRITE);
            FileStream fs = File.OpenRead(fullfilename);
            byte[] buf = new byte[fs.Length];
            fs.Read(buf, 0, (int)fs.Length);
            MessageBox.Show(conn.State.ToString());
            lo.Write(buf);//错误提示出：ERROR: 42704: invalid large-object descriptor: 0
            fs.Close();
            lo.Close();
            NpgsqlCommand command = new NpgsqlCommand("insert into file2(name, content) values(@name, @content)", conn);
            command.Parameters.Add(new NpgsqlParameter("@name", NpgsqlTypes.NpgsqlDbType.Text));
            command.Parameters.Add(new NpgsqlParameter("@content", NpgsqlTypes.NpgsqlDbType.Integer));
            command.Parameters["@name"].Value = filename;
            command.Parameters["@content"].Value = noid;
            command.ExecuteNonQuery();
            transaction.Commit();
            conn.Close();
            MessageBox.Show("上传文件成功！");
        }
      
        private void button2_Click(object sender, EventArgs e)
        {
            SaveFileDialog sfd = new SaveFileDialog();
            if (sfd.ShowDialog() == DialogResult.OK)
            fullfilename = sfd.FileName.ToString();
            filename = Path.GetFileName(fullfilename);
            NpgsqlConnection conn = new NpgsqlConnection("server=127.0.0.1;database=mydb;uid=postgres;pwd=1234");
            conn.Open();
            NpgsqlTransaction transaction = conn.BeginTransaction();
            LargeObjectManager lom = new LargeObjectManager(conn);
            conn.Open();
            //NpgsqlDataAdapter sda = new NpgsqlDataAdapter("select * from file2 where name = '" + filename + "'", conn);
            //DataSet ds = new DataSet();
            //sda.Fill(ds, "file2");
            //int noid = (int)ds.Tables["file2"].Rows[0][1];
            NpgsqlCommand cmd = new NpgsqlCommand("select content from file2 where name = '" + filename + "'", conn);
            NpgsqlDataReader sdr = cmd.ExecuteReader();
            int noid = sdr.GetInt32(1);
            LargeObject lo = lom.Open(noid, LargeObjectManager.READ);
            FileStream fs = File.OpenWrite(fullfilename);
            byte[] buf = new byte[lo.Size()];
            buf = lo.Read(lo.Size());
            fs.Write(buf, 0, (int)lo.Size());
            fs.Flush();
            fs.Close();
            lo.Close();
            transaction.Commit();
            DeleteLargeObject(noid);
            //MemoryStream ms = new MemoryStream(buf);
            //pictureBox1.Image = Image.FromStream(ms);
            conn.Close();
            MessageBox.Show("上传文件成功！");
        }
        public static void DeleteLargeObject(Int32 noid)
        {
            NpgsqlConnection conn = new NpgsqlConnection("server=127.0.0.1;database=mydb;uid=postgres;pwd=1234");
            conn.Open();
            NpgsqlTransaction t = conn.BeginTransaction();
            LargeObjectManager lom = new LargeObjectManager(conn);
            lom.Delete(noid);
            t.Commit();
            conn.Close();        }