我有一个方法，我用Parallel.ForEach来加快处理，首先它是挑选小文件和处理速度快;对于大文件，它非常慢，比for循环慢。我该如何提高速度，或者我应该尝试不同的方法？
请建议或指导我如何提高速度。

public bool CheckQueueExist()
{
    try
    {
        if (QueueVariables.NewFolderPath == "")
        {
            LoadFilePath();
        }
        string path = QueueVariables.NewFolderPath;
        DirectoryInfo info = new DirectoryInfo(path);
        var files = info.GetFiles().OrderBy(p => p.CreationTime)
            .ThenBy(a => a.Name).Take(10000).ToArray();

        var batchOfFiles = files
            .Select((x, i) => new { Index = i, FullName = x.FullName, Name = x.Name })
            .GroupBy(x => x.Index / 10)
            .Select(x => x.Select(v => new { v.Name, v.FullName }).ToList())
            .ToList();

        bool commitstatus = false;

        Parallel.ForEach(Partitioner.Create(
            batchOfFiles, EnumerablePartitionerOptions.NoBuffering),
            new ParallelOptions() { MaxDegreeOfParallelism = 2 }, batch =>
        {
            StringBuilder strQueryBuild = new StringBuilder();
            List<string> filenamesToMove = new List<string>();

            foreach (var file in batch)
            {
                string fullfilepath = file.FullName;
                string Filename = file.Name;
                try
                {
                    string content = System.IO.File.ReadAllText(fullfilepath);
                    strQueryBuild.Append(content);
                    filenamesToMove.Add(fullfilepath);
                }
                catch (Exception ex)
                {
                    commitstatus = false;
                    AppHelper.ErrrorLog(ex, "File in USE: " + fullfilepath);
                }
            }

            int RowsAffected = 0;
            try
            {
                string connstr = System.Configuration.ConfigurationManager
                    .ConnectionStrings["XYZ"].ConnectionString;
                using (var conn = new NpgsqlConnection(connstr))
                {
                    conn.Open();
                    var tra = conn.BeginTransaction();
                    try
                    {
                        NpgsqlCommand cmd = new NpgsqlCommand();
                        cmd.Connection = conn;
                        cmd.CommandType = CommandType.Text;
                        cmd.CommandTimeout = 0;
                        cmd.CommandText = strQueryBuild.ToString();
                        RowsAffected = cmd.ExecuteNonQuery();
                        if (RowsAffected == 0)
                        {
                            RowsAffected = 1;
                        }
                        tra.Commit();
                        commitstatus = true;
                    }
                    catch (Exception ex)
                    {
                        AppHelper.ErrrorLog(ex, "UploadFileData-Error1");
                        RowsAffected = -1;
                        tra.Rollback();
                        commitstatus = false;
                    }
                }
            }
            catch (Exception ex)
            {
                commitstatus = false;
                AppHelper.ErrrorLog(ex, "ProcessQueue-Error2");
            }

            if (commitstatus)
            {
                Parallel.ForEach(filenamesToMove, filepath =>
                {
                    string Filename = Path.GetFileName(filepath);
                    MovetoSuccessFolder(filepath, Filename);
                });
            }
            else
            {
                Parallel.ForEach(filenamesToMove, filepath =>
                {
                    string Filename = Path.GetFileName(filepath);
                    MovetoFailureFolder(filepath, Filename);
                });
            }
        });

        return commitstatus;
    }
    catch (Exception ex)
    {
        AppHelper.ErrrorLog(ex, "CheckQueueExist");
        return false;
    }
    finally
    {

    }
}