Why does PHP send it all at once? [duplicate]

Answer 1

Using 'flush' might work on some webservers / browsers (meagar is correct that it won't work while output buffering is enabled - but that doesn't mean it will work the rest of the time).

It's up to the webserver to decide when to revert to chunked encoding - most will start a chunked response when you call flush as long as you're not compressing the output stream. Then it's up to the browser to decide when it starts rendering an incomplete response - and behaviour will vary depending on the content too - e.g. none will start rendering a table until it has the closing tag.

A better solution then trying to handle it in the receiving page, is to handle it in the sending page - e.g. using a litebox to display the message. Alternatively the message could be presented in an interim page which does a redirect to the generated content.

Answer 2

By default, PHP will buffer your output and send a fewer number of larger chunks to the user. You can use flush to send the contents of write buffer to the user immediately:

<p id="loading_msg">Loading...</p>

<h1>Hello</h1>
<?php
    flush();
    sleep(2);

This won't work if you've previously enabled output buffering by calling ob_start or the php.ini directive output_buffering to 1.