How to find memory used by an object in PHP? (sizeof)

Question

How to find memory used by an object in PHP? (c's sizeof). The object I want to find out about is a dictionary with strings and ints in it so it makes it hard to calculate it manually. Also string in php can be of varied length depending on encoding (utf8 etc) correct?

Solution 1

You could use memory_get_usage().

Run it once before creating your object, then again after creating your object, and take the difference between the two results.

Solution 2

To get an idea about the objects size, try

strlen(serialize($object));

It is by no means accurate, but an easy way to get a number for comparison.

Solution 3

If you need to know the size of an already created object or array, you can use the following code to find it out.

<?php

function rec_copy($src) {
  if (is_string($src)) {
    return str_replace('SOME_NEVER_OCCURING_VALUE_145645645734534523', 'XYZ', $src);
  }

  if (is_numeric($src)) {
    return ($src + 0);
  }

  if (is_bool($src)) {
    return ($src?TRUE:FALSE);
  }
  if (is_null($src)) {
    return NULL;
  }

  if (is_object($src)) {
    $new = (object) array();
    foreach ($src as $key => $val) {
      $new->$key = rec_copy($val);
    }
    return $new;
  }

  if (!is_array($src)) {
    print_r(gettype($src) . "\n");
    return $src;
  }

  $new = array();

  foreach ($src as $key => $val) {
    $new[$key] = rec_copy($val);
  }
  return $new;
}

$old = memory_get_usage();
$dummy = rec_copy($src);
$mem = memory_get_usage();

$size = abs($mem - $old);
?>

This essentially creates a copy of the array structure and all of its members.

A not 100% accurate, but still working version is also:

<?php

$old = memory_get_usage();
$dummy = unserialize(serialize($src));
$mem = memory_get_usage();

$size = abs($mem - $old);

Hope that helps for cases where the object is already build.

Comments

[NickT]

You forgot to wait for April 1st to post this one mate!

[Stann]

i don't think he was serious:)

[danorton]

That might have some uses, but not for memory. PHP <= 5.2 is profoundly inefficient in the way that it stores some memory structures.

[Mathieu Dumoulin]

Another way to do it while in memory is to get the memory usage, clone the object, get the new memory usage and unset the clone. There is a footprint though, so don't abuse... :)

[Neocortex]

I believe the result that we are getting from the echo memory_get_usage() before and after an array, its units suppose to be in KB!!! I divided the memory size by 1024! To get actual memory size consumed.

[Alex]

Not so insane thought. I think what Peter said could be turned into something functional...probably a recursive function that will gradually go deeper into the object and collect and sums all the size of variables. Could be useful for debug purposes....

[Alex]

Yeah? Well, what if PHP decides to play with the memory just before calling the second memory_get_usage?...very brittle solution....

[userfuser]

This object cloning principle may not work so well for smaller objects. When I tested a bit, my PHP seemed to be acquiring new pieces of RAM only in chunks of 256 KB, or at least that was what I received from memory_get_usage(). So, if your object would be 20KB, you'd need to create cca. 10 of them, just to get the memory_get_usage() to change.

[userfuser]

Far from insane or a joke, but still very imprecise unless done thoroughly and properly. Anyway, it could easily get you very good idea of what is eating your RAM the most (if some var is spending 40% or more of your RAM - you would notice it with this)

[clod986]

I was using this to check the json response before sending it, but it actually exhausts my memory limit

[Platinum Fire]

This answer has been debunked on multiple questions already, as memory_get_usage() gets the used memory of the entire PHP script and does not separate things like overheads, ergo comparing it's results does not give you the size of the object.

[Yousha Aleayoub]

actually memory_get_usage(FALSE) or you will get allocated memory

[Himanshu Upadhyay]

this will give size in bytes or what?

[fede72bari]

if you want to detect which is the object that takes the system memory over the limit, your process double even if temporarily the used amount of memory pushing the system even before overload

[fede72bari]

if you want to detect which is the object that takes the system memory over the limit, your process double even if temporarily the used amount of memory pushing the system even before overload