In ASP, the Response object sends output to the client browser. You can use the Response.Buffer property to indicate whether the page output is buffered. If buffered, all scripts on the page will finish processing unless you specifically call either the Flush or End method. You can set the buffer in IIS or in code using the Buffer property.

For example:

Response.Buffer = True

If the Response.Buffer property is set to True, the Flush method immediately sends all current buffered page content to the client. IIS then stops processing ASP code and waits for the browser to ping back (a very fast procedure). The use of Response.Flush is a fairly common technique for showing a page background image and page header nearly immediately to a visitor while the rest of the page is rendered. This gives visitors the feeling of a more responsive website.

Proper Use of Flush:

Response.Buffer = True
''' ...some code that outputs here (perhaps a header and body background image)
Response.Flush

Note: If the Flush method is called, the server does not honor Keep-Alive requests for that page.

If Buffering is Off, Flush Returns an Error

If Response.Buffer is False, then Flush will return the following runtime error.

Response object error 'ASP 0157 : 80004005' 
Buffering On 
/home.asp, line 15 
Buffering cannot be turned off once it is already turned on. 

Response.Buffer Default

In IIS 5 and above, the default for Response.Buffer is True. In IIS 4 and earlier, the default was False.

Redirects MUST come before Flush

However, once you've called Response.Flush, you cannot use Response.Redirect to redirect to another page. Therefore, all your processing that might lead to a redirect needs to occur BEFORE you call Response.Flush. I think that's okay, because your code is cleaner anyway.

This code will fail...

Response.Flush
Response.Redirect "/"

With this error:

Response object error 'ASP 0156 : 80004005' 
Header Error 
/aspsuite/estore/_opensupportaccount.asp, line 47 
The HTTP headers are already written to the client browser.
Any HTTP header modifications must be made before writing page content. 

Cookies and Flush

Because cookies must be written before any HTML output, you need to handle cookies prior to calling Response.Flush.

Calling Flush Multiple Times

You can use Response.Flush to show the top of your page so your visitor can start reading your page. This is a common technique around tables. Because browsers render ONLY after an end table tag, it is a common technique to call Response.Flush after the table end tag and prior to starting a new table.

You can call Response.Flush as many times as you want. However, because the browser must ping back to the server, it is a best practice to limit the use of Response.Flush to just a few per page. You definately don't want to call it every time you loop through a table of say 1,000 records.