You want to force output to be sent to the browser. For example, before doing a slow database query, you want to give the user a status update.
Use flush( ), as in Example 8-29.
Flushing output to the browser
The flush( ) function sends all output that PHP has internally buffered to the web server, but the web server may have internal buffering of its own that delays when the data reaches the browser. Additionally, some browsers don't display data immediately upon receiving it, and some versions of Internet Explorer don't display a page until it has received at least 256 bytes. To force IE to display content, print blank spaces at the beginning of the page, as shown in Example 8-30.
Forcing IE to display content immediately
8.11.4. See Also
Recipe 23.13; documentation on flush( ) at http://www.php.net/flush.