CODEWITHSUNDEEP
phpmemory-management
kingmaple
kingmaple

Reputation: 4320

Why does a simple PHP unset() memory test utilize twice the amount of memory in PHP 5.3?

I was testing out whether unset() affects memory while the script is running, to see if unset() or other known method, $var=null is more efficient. unset() did affect memory, but since I tested it out on two different virtualhosts, I wondered why does one take more or less twice the amount of memory for the same script? I'm guessing the answer is something simple, but it escapes me at the moment. Script itself is below:

<?php

$init=memory_get_usage();
$test=array();
for($i=0;$i<=100000;$i++){
    $test[$i]=rand(0,10000000);
}
echo 'MEMORY CHANGE: '.((memory_get_usage()-$init)/1024/1024).'MB<br/>';

for($i=0;$i<=100000;$i++){
    unset($test[$i]);
}
echo 'MEMORY CHANGE: '.((memory_get_usage()-$init)/1024/1024).'MB<br/>';

//output on PHP 3.2.5 virtualhost:
//MEMORY CHANGE: 6.98558807373MB
//MEMORY CHANGE: 0.500259399414MB

//output on PHP 5.3.5 virtualhost
//MEMORY CHANGE: 13.970664978MB
//MEMORY CHANGE: 1.00063323975MB

?>

Thanks!

Upvotes: 4

Views: 340

Answers (1)

Marc B
Marc B

Reputation: 360782

PHP 3.2.5? That's so old it doesn't even reach the stone age. PHP's guts underwent a total re-write with the Zend engine, so even though the language itself stayed relatively the same, you're comparing two different environments.

But in case that version number is a typo, then possibly it's a 32bit v.s. 64bit host, which doubles the size of ints and could account for your purported 2x difference.

Upvotes: 3

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