Question

I am attempting to write out an Excel file from an ASP.NET web server using OpenXML. I have about 2100 records and its taking around 20-30 seconds to do this. Any way I can make it faster? Retrieving the 2100 rows from the db takes a fraction of a second. Not sure why manipulating them in memory would take any longer.

Note: ExcelWriter is our custom class, but all its methods are directly from code in this link, http://msdn.microsoft.com/en-us/library/cc861607.aspx

   public static MemoryStream CreateThingReport(List<Thing> things, MemoryStream template)
    {
        SpreadsheetDocument spreadsheet = SpreadsheetDocument.Open(template, true);
        WorksheetPart workSheetPart = spreadsheet.WorkbookPart.WorksheetParts.First();

        SharedStringTablePart sharedStringPart = spreadsheet.WorkbookPart.GetPartsOfType<SharedStringTablePart>().First();

        Cell cell = null;
        int index = 0;

        //create cell formatting for header text
        Alignment wrappedAlignment = new Alignment { WrapText = true };
               uint rowOffset = 2;

  foreach (Thing t in things)
        {
            //Received Date
            cell = ExcelWriter.InsertCellIntoWorksheet("A", rowOffset, workSheetPart);
            index = ExcelWriter.InsertSharedStringItem(t.CreateDate.ToShortDateString(), sharedStringPart);
            cell.CellValue = new CellValue(index.ToString());
            cell.DataType = new DocumentFormat.OpenXml.EnumValue<CellValues>(CellValues.SharedString);

            //Car Part Name
            cell = ExcelWriter.InsertCellIntoWorksheet("B", rowOffset, workSheetPart);
            index = ExcelWriter.InsertSharedStringItem(t.CarPart.Name, sharedStringPart);
            cell.CellValue = new CellValue(index.ToString());
            cell.DataType = new DocumentFormat.OpenXml.EnumValue<CellValues>(CellValues.SharedString);

  rowOffset++; 
   }

 workSheetPart.Worksheet.Save();

        spreadsheet.WorkbookPart.Workbook.Save();
        spreadsheet.Close();

        return template;

Answer 1

So it looks like someone in the MSDN community docs ran into similar performance implications. The code below is very inefficient. Someone recommended using a hash table.

For our solution we just removed the insertion of shared strings altogether and went from 1:03 seconds to 0:03 seconds in download time.

//Old: (1:03)
            cell = ExcelWriter.InsertCellIntoWorksheet("A", rowOffset, workSheetPart);
            index = ExcelWriter.InsertSharedStringItem(thing.CreateDate.ToShortDateString(), sharedStringPart);
            cell.CellValue = new CellValue(index.ToString());
            cell.DataType = new DocumentFormat.OpenXml.EnumValue<CellValues>(CellValues.SharedString);

 //New: (0:03)
             cell = ExcelWriter.InsertCellIntoWorksheet("A", rowOffset, workSheetPart);
             cell.CellValue = new CellValue(thing.CreateDate.ToShortDateString());
              cell.DataType = new DocumentFormat.OpenXml.EnumValue<CellValues>(CellValues.String);

MSDN Docs (slow solution, they should use a Hash Table instead)

      private static int InsertSharedStringItem(string text, SharedStringTablePart         shareStringPart)
  {
// If the part does not contain a SharedStringTable, create one.
if (shareStringPart.SharedStringTable == null)
{
    shareStringPart.SharedStringTable = new SharedStringTable();
}

int i = 0;

// Iterate through all the items in the SharedStringTable. If the text already exists, return its index.
foreach (SharedStringItem item in shareStringPart.SharedStringTable.Elements<SharedStringItem>())
{
    if (item.InnerText == text)
    {
        return i;
    }

    i++;
}

// The text does not exist in the part. Create the SharedStringItem and return its index.
shareStringPart.SharedStringTable.AppendChild(new SharedStringItem(new DocumentFormat.OpenXml.Spreadsheet.Text(text)));
shareStringPart.SharedStringTable.Save();

return i;
 }