php memory usage

Question

It looks like in PHP it requires about 213 bytes to store one integer, is it true? Okay, please take a look on the next code:

$N = 10000;
echo memory_get_usage()."\n";
$v = array();
for($i = 0; $i < $N; $i++) {
    $v[] = $i;
}
echo memory_get_usage()."\n";
unset($v);
echo memory_get_usage()."\n";

Output is next:

641784
2773768
642056

So, the difference is 2773768 - 641784 = 2131984 byte, or 213 byte per integer. why so much? 4 bytes is more than enough.

Mark Baker · Accepted Answer · 2012-06-24 10:37:12Z

3

4 bytes is only enough if you simply store an integer value somewhere in memory, without making any allowance for the fact that it is a variable which needs a datatype identification, flags to indicate if there are any other references to that variable, the name of that variable, etc. all of which require additional memory.

PHP stores the value in a zval* so there's all the additional bytes used to store the zval details in addition to the actual value.

answered Jun 24, 2012 at 10:37

Mark Baker

213k34 gold badges354 silver badges390 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Mark Baker Over a year ago

Note also that 4-bytes for an integer value is correct for 32-bit PHP, if you're using 64-bit then it's 8-bytes

Mark Baker Over a year ago

Note also that you're creating an array, which also has a zval structure, and the hashmap associated with mapping that array to the values it contains also has a memory overhead

Collectives™ on Stack Overflow

php memory usage

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related