Excel Interop - Efficiency and performance

Question

I was wondering what I could do to improve the performance of Excel automation, as it can be quite slow if you have a lot going on in the worksheet...

Here's a few I found myself:

• ExcelApp.ScreenUpdating = false -- turn off the redrawing of the screen

• ExcelApp.Calculation = Excel.XlCalculation.xlCalculationManual -- turning off the calculation engine so Excel doesn't automatically recalculate when a cell value changes (turn it back on after you're done)

• Reduce calls to Worksheet.Cells.Item(row, col) and Worksheet.Range -- I had to poll hundreds of cells to find the cell I needed. Implementing some caching of cell locations, reduced the execution time from ~40 to ~5 seconds.

What kind of interop calls take a heavy toll on performance and should be avoided? What else can you do to avoid unnecessary processing being done?

Answer 1

When using C# or VB.Net to either get or set a range, figure out what the total size of the range is, and then get one large 2 dimensional object array...

//get values object[,] objectArray = shtName.get_Range("A1:Z100").Value2; iFace = Convert.ToInt32(objectArray[1,1]);  //set values object[,] objectArray = new object[3,1] {{"A"}{"B"}{"C"}}; rngName.Value2 = objectArray; 

Note that its important you know what datatype Excel is storing (text or numbers) as it won't automatically do this for you when you are converting the type back from the object array. Add tests if necessary to validate the data if you can't be sure beforehand of the type of data.

Answer 2

This is for anyone wondering what the best way is to populate an excel sheet from a db result set. This is not meant to be a full list by any means but it does list a few options.

Some performance numbers while attempting to populate an excel sheet with 155 columns and 4200 records on an old Pentium 4 3GHz box including data retrieval time which was never more than 10 seconds in order of slowest to fastest is as follows...

1. One cell at a time - Just under 11 minutes

2. Populating a dataset by converting to html + Saving html to disk + Loading html into excel and saving worksheet as xls/xlsx - 5 minutes

3. One column at a time - 4 minutes

4. Using the deprecated sp_makewebtask procedure in SQL 2005 to create an HTML file - 9 Seconds + Followed by loading the html file in excel and saving as XLS/XLSX - About 2 minutes.

5. Convert .Net dataset to ADO RecordSet and use the WorkSheet.Range[].CopyFromRecordset function to populate excel - 45 seconds!

I ended up using option 5. Hope this helps.