Cesar D. Rodas

Write programs in PHP is very easy, that is because PHP syntax is simple and very effective. But also in PHP you must have some concepts for write effective programs, because if you are planing to have a very busy web site that little optimizations tips could help you to handle more visitors and to offload a little the processor.

All test were done in a Intel III PC with GNU/Linux SuSE 10.2, 1GB of RAM memory. All these examples uses the following functions for measure the time of execution:

<?php
function start() {
	global $t;
	$t = time() + (float)microtime();
}

function _time($s) {
	global $t;
	$e = time() + (float)microtime();
	return $s.($e-$t).“ seconds<br/>“;
}

?>

Avoid the Array of Array

An array is a data structure consisting of a group of elements that are accessed by indexing. In most programming languages the array index is a number, but in PHP the key could be anything ( string, integers, floats), that is because PHP does an hash with the index. That is a great feature that can made easy develop flexible programs.

But also that feature could have an negative impact if we usually use “array of array”. Example:

<?php
start();
for($i=0; $i < 60000; $i++)
	$f[‘a‘][‘b‘][$i] = $i;
print _time(“Execution time: “);
?>
Execution time: 0.07426404953 seconds

But sometimes it is necesary to use “array of array” for made the code simpler and more shorter. In this case is a good alternative to use reference to a variable.

<?php
start();
$b = &$f[‘a‘][‘b‘];
for($i=0; $i < 60000; $i++)
	$b[$i] = $i;
print _time(“Execution time: “);
?>
Execution time: 0.0515649318695 seconds

Now we can see than the second string is faster than the first that is because in the first script PHP is doing three hash lookups for every new itineration of the for, and in the second the first time the two lookups are done and save that refence in $b, so in the for only one lookup is done instaed of three.

Do never use array with undeclarated constants

PHP will process $f[a],”a” as a constanst and if “a” is not a constant PHP will process as $f[’a'].

<?php
start();
for($i=0; $i < 60000; $i++)
	$f[a] = $i;
print _time(“Execution time: “);
?>
Execution time: 0.23406291008 seconds

Sould be:

<?php
start();
for($i=0; $i < 60000; $i++)
	$f[‘a‘] = $i;
print _time(“Execution time: “);
?>
Execution time: 0.0413820743561 seconds

As we can see the difference in time execution is very big, the seconds script execute almost 6 times faster than the first, and the only difference are the quotes (singles or double are the same). That is becuase in the first the Index a is a constant and in run-time PHP do an lookup in constants-table and do not find, so then transform that constant into a string.

Loops with arrays

<?php
$array= range( 1, 10000);
start();
for($i=0; $i < count($array); $i++)
	;
print _time(“Execution time: “);
?>
Execution time: 0.0144419670105 seconds

<?php
$array= range( 1, 10000);
start();
$b = count($array);
for($i=0; $i < $b; $i++)
	;
print _time(“Execution time: “);
?>
Execution time: 0.00201916694641 seconds

<?php
$array= range( 1, 10000);
start();
foreach($array as $k => $v);
	;
print _time(“Execution time: “);
?>
Execution time: 0.00279021263123 seconds

We can see that the fist script has lowest perfomance that is because for every itineration the for is calling the “count” function and is counting the lenght of the array. In the second script the “count” is calling only one time and save in $b, that is the fasted solution because usually arrays do not change their length on loops. And the third function has higher time executing than the second and lowest than the first but it is the best (i think) for itinerate arrays with non-numerical index.

Do you know other tips?

Please let us know, write down your own tips!

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This entry was posted on Saturday, September 29th, 2007 at 5:51 pm and is filed under PHP, servers, phpclasses. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.