Bug #65723 [Nab]: Memory limit of string

[m dot banaszek at smartmedia dot com dot pl]

Edit report at https://bugs.php.net/bug.php?id=65723&edit=1

 ID:                 65723
 User updated by:    m dot banaszek at smartmedia dot com dot pl
 Reported by:        m dot banaszek at smartmedia dot com dot pl
 Summary:            Memory limit of string
 Status:             Not a bug
 Type:               Bug
 Package:            Scripting Engine problem
 Operating System:   Windows 8
 PHP Version:        Irrelevant
 Block user comment: N
 Private report:     N

 New Comment:

Hello,
i'm very sorry there should be line : "$string .= $strb; ".
I tested your simplified code on my production machine. For 50 tests script 
fail 
always on 480MB
I use windows serwer 2008 r2 x64, iis 7, php 5.4.14.
When use array for test memory usage grows up to 1,9GB as expected.
I found temporary solution "http://www.ntcore.com/4gb_patch.php";.
after patch, string test use 1,5 GB memory and array over 3GB


Previous Comments:
------------------------------------------------------------------------
[2013-09-20 20:58:47] ahar...@php.net

There are some issues with your test: in its default "string" mode, memory 
usage 
never actually increases. If I change it to "array" mode, it behaves how the 
manual says it will — 81 iterations succeed ($strb is 10,000,000 bytes in 
size, 
and the effective memory limit is 838,860,800 bytes), and then the script 
errors 
out with an out of memory error (there are 810,000,000 bytes in the array, plus 
overhead for the array itself, plus $strb, plus general overhead). Bear in mind 
that the memory limit applies to the entire runtime, not individual variables.

A simpler, clearer test is this:

<?php
ini_set('memory_limit', '800M');
$buffer = '';

while (true) {
    $buffer .= str_repeat(' ', 10000000);
    printf("Length of buffer: %d\nMemory usage: %d\n", strlen($buffer), 
memory_get_usage());
}
?>

In short, this behaves as expected and documented.

------------------------------------------------------------------------
[2013-09-20 11:24:10] m dot banaszek at smartmedia dot com dot pl

Description:
------------
The PHP manual now states, that strings are limited to 2GB. However in test 
script, I specify a memory limit to 800MB. I wrote a PHP application where 
memory 
usage is growing over time. Unfortunately the size of a single string variable 
doesn't  exceed memory limit of 300-400MB and my test stops. Testing my script 
on 
5.4.17,18,19 and  5.3.10 of PHP versions, but any of this versions don't 
supported  my memory limit or 2GB memory.

Test script:
---------------
<?php
ini_set('memory_limit', '800M');
$string = '1234567890';
$strb = '';
for ($i = 0; $i < 1000000; $i++)
    $strb .= $string;
$arr = array();
$i = 0;
$testType = 'string'; //'array'
while (1) {
    $i++;
    if ('string' == $testType) {
        error_log((strlen($string) / 1000000) . ' - ' .
                (memory_get_usage() / 1000000));
    } else {
        $arr[] = $strb . $i;
        error_log((strlen($string) / 1000000) . ' - ' .
                (memory_get_usage() / 1000000));
    }
    error_log((count($arr)) . ' - ' . (memory_get_usage() / 1000000)); }

Expected result:
----------------
Memory usage grow to about 800MB.

Actual result:
--------------
Memory error of 300-400MB. So the memory usage does not continually grow to 
800MB.


------------------------------------------------------------------------



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Edit this bug report at https://bugs.php.net/bug.php?id=65723&edit=1