I use and OleDbDataReader inside using but the memory is never released.
I close the reader after use.

public void getSegmentData(string tag, string outputPath, string databaseName, Log log)
{
OleDbCommand command = null;

        try
        {
            using (OleDbConnection connection = new OleDbConnection("Data Source=.\WINCC;User ID=Localadmin;Provider=WinCCOLEDBProvider.1;Persist Security Info=False;Catalog=" + databaseName + ";Mode=Read"))
            {
                command = new OleDbCommand("TAG:R," + "'" + tag + "'" + ",'2005-01-01 00:00:00.000','2035-12-31 23:59:59.000'", connection);
                command.Connection.Open();
                
                using (StreamWriter csvWriter = new StreamWriter($"{outputPath}.csv", false))
                {
                    OleDbDataReader reader = command.ExecuteReader();
                    csvWriter.WriteLine("ValueID;Timestamp;RealValue;Quality;Flags");


                    //vérifie si le fichier est vide
                    if (!reader.HasRows)
                    {
                        log.AddLog(Log.LogType.TRACE, "Le fichier généré pour la variable " + tag + " est vide");
                    }

                    while (reader.Read())
                    {
                        string valueId = reader[0].ToString();
                        string timestamp = reader[1].ToString();
                        string realValue = reader[2].ToString();
                        string quality = reader[3].ToString();
                        string flags = reader[4].ToString();

                        csvWriter.WriteLine($"{valueId};{timestamp};{realValue};{quality};{flags}");

                    }
                    reader.Close();

                    if (reader.IsClosed != true)
                    {
                        log.AddLog(Log.LogType.ERROR, "READER is close != TRUE");
                    
                    }
                }
                command.Connection.Close();
                command.Dispose();
            }
        }