PHP while with sleep loop not updating database until end of loop

Question

I have a while loop with a sleep function that I wan´t to run -> update database -> sleep -> run again for a number of 10 times. With the below script the script loops 10 times, but it only updates the database when all 10 loops have finished.

I added an echo at the end just to verify, and the echo does not appear on the page until the and when every loop is echoed out at once.

I have also tried placing ob_flush() and flush() after the echo with no luck.

Script

$loops = 10;
while ($loops > 0)
{
  while($row = mysql_fetch_array($result))
  {
    // Get current User status
    $username = $row['username'];
    $user_status = $row['user_status'];
    $user_updated = date('Y-m-d H:i:s');

    // Update database
    $update_sql = "UPDATE  `database`.`user` SET  `user_status` =  '$user_status',
                                                  `user_updated` =  '$agent_updated'
                                            WHERE  
                                                  `user`.`username` =  '$username'";
    $update=mysql_query($update_sql);
    echo "Loop #".$loops."<br>";
  }
flush();
$loops--;
Sleep(5);
}

I've also tried the same with a FOR loop.
Any suggestions would be appreciated. I've gone through the search and haven´t found users with similar issues but I couldn't find the answer.

You can't get echoes one by one. What PHP does is output the entire thing at once, not one part at the time. So in turn, you'll wait for sleep() amount of seconds before you see the output on your screen. — N.B.
If PHP only returns the output at the end, would you recommend haveing a seconds script that calls this page in a loop (calls the page every 5 seconds)? — Skuli Axelson
That's one way to do it, however I don't know what your actual goal is. There is always more than one way to do something, you should describe what you have and what you want, maybe you'll get useful input from other people :) — N.B.
Are you sure that it updates the database when all 10 loops have finished? Or do you just see the last update in db? Is it right to have one while cycle inside of the other one? Where is the $result coming from? — jcjr
Good question. with every update there is a time-stamp in the database so I can monitor the update while the page is looping. The echo at the end of the loop also only returns the ech after all the loops. I also tried using a FOR loop and then a WHILE loop with no change. — Skuli Axelson

Aitor Calderon Aitor Calderon · Accepted Answer · 2012-11-27T16:33:08

You can get those echoes to show one by one, but on a controlled environment (according to php documentation, flush may still buffer the output on several Win32 systems), you can read further in the php flush manual page.

To be more specific, make sure APaches mod_gzip is disabled, also, some php.ini settings like output_buffering and zlib.output_compression should be set to false.

output_buffering = false
zlib.output_compression = false

Even with all of this, you may also need to send a "big" amount of data (like 2048 chars) in order to make some browser to actually display new data.

echo "One"
echo str_repeat(" ", 2048);
Sleep(3)
echo "Two"
echo str_repeat(" ", 2048);
// Ans so on

In the comments of the aforementioned manual page, you can see more examples.

PHP while with sleep loop not updating database until end of loop

3 Answers