PHP var_sizeof()

Function for getting size of any PHP variable in bytes.
It must be more accurate tool to calculate total size of PHP variable than memory_get_usage(), but it has restrictions.

How it works

var_sizeof() with var_class_sizeof() uses FFI to access internal structures of PHP variables.
It calculates the size of internal structures such as zval, _zend_array, _zend_object, etc., as well as additional allocated memory for them.
It doesn't take into calculate the memory of handlers/functions/etc.

Requirements

• PHP >= 7.4 (with FFI)
• Linux(x86_64) / Darwin(x86_64)

How to install

composer require mrsuh/php-var-sizeof

Functions

int var_sizeof(mixed $var);

int var_class_sizeof(mixed $var);

Usage

<?php

require_once __DIR__ . '/vendor/autoload.php';

$int = 1;
printf("variable \$int size: %d bytes\n", var_sizeof($int));

$array = array_fill(0, 100, $a);
printf("variable \$array size: %d bytes\n", var_sizeof($array));

$object = new \stdClass();
printf("variable \$object size: %d bytes\n", var_sizeof($object));
printf("class \$object size: %d bytes\n", var_class_sizeof($object));

var_sizeof vs memory_get_usage

PHP 8.1.2 Linux(x86_64)

type	var_sizeof(bytes)	memory_get_usage(bytes)
NULL	16	0
boolean(true)	16	0
integer(1)	16	0
double(1.5)	16	0
string("hello world")	27	40
resource	48	416
callable	72	384
array(count: 0, list: true)	336	0
array(count: 100, list: true)	2,128	8,248
array(count: 1,000, list: true)	16,464	36,920
array(count: 10,000, list: true)	262,224	528,440
array(count: 100, list: false)	5,192	8,248
array(count: 1,000, list: false)	41,032	41,016
array(count: 10,000, list: false)	655,432	655,416
EmptyClass{}	72	40
ClassWithArray{"array(count: 0, list: true)"}	408	56
ClassWithArray{"array(count: 100, list: true)"}	2,200	8,304
ClassWithArray{"array(count: 1,000, list: true)"}	16,536	36,976
ClassWithArray{"array(count: 10,000, list: true)"}	262,296	528,496
ClassWithObject{"EmptyClass{}"}	144	96
ArrayIterator{"array(count: 100, list: true)"}	2,264	8,376
ArrayIterator{"array(count: 100, list: false)"}	5,328	40,376

type	var_class_sizeof(bytes)	var_sizeof(bytes)	memory_get_usage(bytes)
EmptyClass{}	1,362	72	40
ClassWithArray{"array(count: 0, list: true)"}	1,494	408	56
ClassWithArray{"array(count: 100, list: true)"}	1,494	2,200	8,304
ClassWithArray{"array(count: 1,000, list: true)"}	1,494	16,536	36,976
ClassWithArray{"array(count: 10,000, list: true)"}	1,494	262,296	528,496
ClassWithObject{"EmptyClass{}"}	1,495	144	96
ArrayIterator{"array(count: 100, list: true)"}	2,437	2,264	8,376
ArrayIterator{"array(count: 100, list: false)"}	2,437	5,328	40,376

⚠️ Restrictions

• works correctly only with userland objects and SPL \ArrayIterator
• doesn't work correctly with complicated structures like extensions/resources/callables/functions
• to calculate total size of an object you need to use var_sizeof() with var_class_sizeof()

For contributors

How to reproduce a table of numbers above

git clone --recurse-submodules git@github.com:mrsuh/php-var-sizeof.git && cd php-var-sizeof
composer install
docker build -t image-php-var-sizeof .
docker run -it --rm --name my-running-script -v "$PWD":/app image-php-var-sizeof php bin/render-table.php

How to compile library

cd php-src
./buildconf
./configure
cd ..
make DEBUG=1