MySQL查询执行率

Question

I am making a live chat, which involves long-polling to receive messages asap. However, since afaik web sockets are not supported cross-platform, and i couldnt find a true long polling chat example, i made a similar thing, which i am actually not sure in.

What i do is i call the script in background, which executes query each 200ms until new message appears. And this is the thing im curious about - do i execute it too often? Lets say i have around 100 ppl using this chat so it will be like 500 queries per second. How will this affect the server perfomance? Posting code im using below:

while (($x < 99) && ($allowloop))
{
  $query = mysqli_query($con, 'SELECT * FROM messages');
  if (mysqli_num_rows($query) == 0)
  {
    usleep(200000);
    $x = $x + 1;
  } else {
    $allowloop = false;
  }
}

#processing results

Any tips and suggestions appreciated

Answer 1

You do not want to do this, for the reasons you already know.

What you need is some change, a client's browser can detect, that signals a new message is present. This could be the presence of a file (with the new message?), or a string in a file.

So what you could do is:

1. A new message is available on the server.
2. The server sets the flag, either a file, or a string in a file.
3. The client browser polls the small file, checking for the flag.
4. If the flag is detect, the new message is shown.

Polling once every few seconds is more than fast enough for chatting. This method means that the clients browser doesn't invoke a MySQL query every time a check is done.

In all other cases I would use something like: http://nodejs.org