Upper memory limit for PHP/Apache

Question

I'm getting the error when I run my PHP script....

Fatal error: Out of memory (allocated 1827405824) (tried to allocate 88800 bytes)

I've added this line to my PHP script..

ini_set("memory_limit","3000M");

This statement does seem to correctly control the memory usage, but I dont seem to be able to get it above about 1.8GB. Its as if the upper memory limit is being restricted somewhere else. I've also added to the php.ini...

memory_limit = 3000M

Does anyone know if the memory is restricted elsewhere?

I'm running a local server with Xampp. I have Windows 7, 64-bit with 4GB RAM. My script uses PHP's GD image library and I get the error when trying to allocate an image reference with ImageCreateTrueColor().

(I know this is a huge amount of memory - but this is just a one-of script, and its just a lot easier to do it this way.)

Thanks.

Update....

@elusive @Orbling I expect everybody's bored whith this question, but here is the simplified code which illustrates the problem.

<?php
    ini_set("memory_limit","4000000000");
    echo "ini_get = " . ini_get('memory_limit') . "<br>
";
    echo "memory_get_usage = " . memory_get_usage(true) . "<br>
";
    $bigImageHandle = imagecreatetruecolor(22200, 24800);  //this is line 5
?>

Browser output...

ini_get = 4000000000
memory_get_usage = 524288

Fatal error: Out of memory (allocated 1843396608) (tried to allocate 88800 bytes) in
E:UserMy_WebsexperimentshouseshuntingemposMaps1.php on line 5

I tested this out with a smaller set of tiles and the memory used by imagecreatetruecolor() and I estimate I need 2.7GB

Answer 1

You're running on a 64-bit operating system, but Apache and PHP are likely still 32-bit. If you're using mod_php, apache would be the limiting factor here.

32-bit processes are limited about 2GiB of RAM unless you used the /3GB switch and the software is aware of 3GB support.

That still leaves up about 200 MiB that seems unused, but its small enough that it can be used by various libraries that all have to be loaded in memory

As far as I know, the library usage won't show up in the committed memory, but still counts towards the 2GiB limit (much like device memory counts towards the 4GiB limit on 32-bit windows. Where installing 2 GiB graphics card brings you down to under 2GiB of usable RAM).

Most likely solution? Install a 64-bit PHP, and then dispatch it to that (using a system() call, perhaps)