big_php_arrays_are_bad.php

<?php

// Example to accompany blog post: 
// http://blog.banksdesigns.co.uk/post/when-not-to-use-arrays-in-php

ini_set('memory_limit', '512M');

$array_2d = $array_strings = array();

$mem_start = memory_get_usage();

for ($i = 0; $i < 250000; $i++)
{
	$array_2d[] = array(123,321,234,654);
}

$mem_2d = memory_get_usage();
print "Memory for 2D:\t\t".round(($mem_2d - $mem_start)/1048576, 2)."MB\n";

for ($i = 0; $i < 250000; $i++)
{
	$array_strings[] = '123,321,234,654';
}

$mem_strings = memory_get_usage();
print "Memory strings:\t\t".round(($mem_strings - $mem_2d)/1048576, 2)."MB\n";

// Speed test - change the third element for each value to 999

$start_time = microtime(TRUE);

foreach ($array_2d as $id => $values)
{
	$array_2d[$id][2] = 999;
}

$time_2d = microtime(TRUE);
print "Time for 2D:\t\t".round($time_2d - $start_time, 2)." seconds\n";

foreach ($array_strings as $id => $values)
{
	$values = explode(',', $values);
	
	$values[2] = 999;
	
	$array_strings[$id] = implode(',', $values);
	
}

$time_strings = microtime(TRUE);
print "Time strings:\t\t".round($time_strings - $time_2d, 2)." seconds\n";