MySQL and PHP: How to make it work without killing your server

Introduction

There are currently over 25 Million websites powered by PHP. If you
had the time (and patience, nevermind the means) to check all of
them, you would most certainly find that most use PHP in
conjunction with a MySQL Database. The reasons for this is simple:
they work extremely well together, they are relatively simple to
integrate and they are flexible.

But in PHP’s flexibility lies its greatest weakness. Just because it
allows you to do almost anything you like in just about any way you
like, does not mean that you are code is performing at it’s best.
If it has not happened to you already, the day will come that you start
to ask yourself why your script is so slow, even on localhost!

Until you properly understand what happens in the background–on the
server–while your code is being processed, you will not have the
tools to eliminate slow server responses. I am not, however, talking
about the actual machine process that happens on the server. I am
simply talking about what happens when you type echo, or print, or
foreach. What are you telling PHP to do?

Just before we actually get into it, a little note: This article
assumes a basic level of understanding of PHP and MYSQL. We will not
be rooting through the basics of coding before getting to our points.
However, I will try to keep things as simple as possible as
this topic is relative to developers of all levels.

PHP: Print, Echo, Strings, Variables and Loops

You will have undoubtably heard of the cardinal rule regarding
echo vs. print. Certainly, I dont think any
discussion on server resources would be complete without it. Its
simple:


    print $variable;


is slower than


    echo $variable;


However, this difference is neglegible. My own script timer could not
accurately time one faster than the other in a script that printed a
simple string ten thousand times.

The crux of the matter lies in the fact that print always
returns true, so that you can do things like:


    $ret = print 'hello world';


and $ret will be 1. You can also do things like


    $b ? print "true" : print "false";


According to the PHP Manual, print is also part of the precedence table which it needs to be if it
is to be used within a complex expression. It is just about at the
bottom of the precedence list though. Only “,” AND,
OR and XOR are lower. In my mind the much more
important fact comes in use: print can only pass one paramater,
where echo can pass multiple parameters. So, you could say:


    echo $variable, $variable2, $variable3, $variable4;


but for the equivalent thing in print:


    print "{$variable} {$variable2} {$variable3} {$variable4}";


Thus, it does not really matter which one you use, although the fact
that print actually returns true, every time it is
used, does seem like a waste of resources to me. If all you are trying
to do is simply print some text to the screen, use echo.

On the topic of strings, it is a well known fact that the following
examples are all valid:


    echo "Hello World, this is my list: {$variable}, {$variable2}, {$variable3}, {$variable4}.";

    echo "Hello World, this is my list: ".$variable.", ".$variable2.", ".$variable3.", ".$variable4.".";

    echo 'Hello World, this is my list: '.$variable.', '.$variable2.', '.$variable3.', '.$variable4.'.';


but the fastest, lightest way of doing this is the third example. This
is because PHP does not bother trying to parse anything inside single
quotes, so it simply ignores the string part and just echoes the
contents to the screen without really caring what they are. Then it
parses the values outside of the single quotes normally. Again,
these results are negligable should you be using a very small page,
but on monolith frameworks that load something like 500 pages per
individual pageload, these things certainly do add up.

Something to remember regarding for loops is that the maximum
boundary should be calculated and stored inside a variable like this:


    $max = count($var);

    for($i=0; $i
    {

      // do something

    }


rather than


    for($i=0; $i
    {

      // do something

    }


Because in the second instance the maximum boundary is calculated
through every iteration of the loop, severely wasting server resources.

Something else I would like to touch on lightly before moving on is
that it is heavier on server resources to keep switching php on and off
inside a script than to just print or echo the html. So, instead of this:


  <?php

    if(isset($var)){ ?>

      <p>hello world</p>

  <?php

    }

  ?>


just do the following:


  <?php

    if(isset($var)){

       echo '<p>hello world</p>';

    }

  ?>


The idea is that opening and closing PHP twice uses more resources
than just echoing a string once.