Csv download getting very slow in VB.NET

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Hi All,
I need to download csv file from asp.net with vb.net
i have done the download csv file from vb.net
The moment i raise you that, when i download less than 50 rows then the file download very fast but when i download more than 100 rows then it has come very slow (means come around after 5 minutes because data is very huge)
So what is the essential step i need to handle for this issue resolved.

Please find my code below,

Using dt As New DataTable()
                  Adp.Fill(dt)

                  'Build the CSV file data as a Comma separated string.
                  Dim csv As String = String.Empty

                  For Each column As DataColumn In dt.Columns
                      'Add the Header row for CSV file.
                      csv += column.ColumnName + ","c

                  Next

                  'Add new line.
                  csv += vbCr & vbLf

                  For Each row As DataRow In dt.Rows
                      For Each column As DataColumn In dt.Columns
                          'Add the Data rows.
                          csv += row(column.ColumnName).ToString().Replace(",", ";") + ","c
                      Next

                      'Add new line.
                      csv += vbCr & vbLf
                  Next

                  'Download the CSV file.
                  Response.Clear()
                  Response.Buffer = True
                  Response.AddHeader("content-disposition", "attachment;filename=SqlExport.csv")
                  Response.Charset = ""
                  Response.ContentType = "application/text"
                  Response.Output.Write(csv)
                  Response.Flush()
                  Response.End()
              End Using

thanks in advance.

regards,
stellus.

What I have tried:

csv download getting very slow in vb.net

Posted 16-Sep-16 21:35pm

stellus

Updated 16-Sep-16 23:57pm

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Comments

Ralf Meier 17-Sep-16 13:08pm

I can't see a generell mistake in your code - sorry. I think, that your problem is the "getting of the data" itself and not your code-construction. Of course : the code could be optimized - but that doesn't solve your "download-Problem" ...

2 solutions

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Mehdi Gholam · Answer 1 · 2016-09-16T21:48:00

Solution 1

Use a StringBuilder() : https://www.dotnetperls.com/stringbuilder-vbnet[^]

Posted 16-Sep-16 21:48pm

Mehdi Gholam

Comments

Karthik_Mahalingam 17-Sep-16 3:49am

5

Mehdi Gholam 17-Sep-16 3:50am

Cheers !

Patrice T · Answer 2 · 2016-09-16T23:57:00

Solution 2

A little trick to speedup your code

VB

Dim csv As String = String.Empty
Dim row_csv As String

...

For Each row As DataRow In dt.Rows
    row_csv = String.Empty
    For Each column As DataColumn In dt.Columns
        'Add the Data rows.
        row_csv += row(column.ColumnName).ToString().Replace(",", ";") + ","c
    Next

    'Add new line.
    row_csv += vbCr & vbLf
    csv += row_csv
Next

Posted 16-Sep-16 23:57pm

Patrice T

Comments

Karthik_Mahalingam 18-Sep-16 2:13am

Good idea, but however StringBuilder() has much better performance,
i have faced it many times

Patrice T 18-Sep-16 4:24am

I know, it is the kind of optimization that was used when string builder did not exist.

Karthik_Mahalingam 18-Sep-16 4:45am

hmm, good to know.

Patrice T 18-Sep-16 5:30am

Repeated addition of a little string to another one involve a workload which grow with the square of the number of operations.
For n operations, the workload is n*(n+1)/2 or (n^2+n)/2.
1 + 2 + 3 + 4 + ⋯ - Wikipedia, the free encyclopedia[^]
In this case say that you have 10 rows and 10 columns.
OP solution gives n=100 with operation size of 1, it gives a workload of 100*101/2=5050
with my solution, building of a row is n=10, size=1 and workload=55
building of the big string is n=10, size=10 (because each row is 10 cells), workload=550
Global workload is 55*10+550=1100
With 100 rows, the gain is even better.