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Date: Tue, 06 Mar 2007 01:43:39 +0300
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Subject: Re: [PHP-DEV] The way the engine works?
From: antony@zend.com (Antony Dovgal)

On 03/06/2007 12:34 AM, Brian Moon wrote:
> Ok, I am no C coder and I don't claim to be very smart about low level 
> parts of PHP.  But, IMO, this is bug.
> 
> http://bugs.php.net/bug.php?id=36924
> 
> I have created a test script that shows the insanity of this bug:
> 
> <?php
> 
> $str = "This is a medium length string";
> 
> $start = memory_get_usage();
> for($x=1;$x<=100;$x++){
>      echo $str.": (3.5): ".time()."\n";
> }
> $first_growth = number_format(memory_get_usage() - $start);
> 
> $start = memory_get_usage();
> for($x=1;$x<=100;$x++){
>      echo "$str: (3.5): ".time()."\n";
> }
> $growth = number_format(memory_get_usage() - $start);
> 
> 
> echo "first growth: $first_growth\nsecond growth: $growth\n";
> 
> ?>

Number of iterations | First growth | Second growth | Peak usage
100                      480 bytes      ~5Kb          ~73Kb
100 000                  556 bytes      ~32Kb         ~100Kb
1 000 000                556 bytes      ~32Kb         ~100Kb

Tested with PHP 5.2.1 and 5.2.2-dev on Linux (with --disable-debug).

> Now, you turn that into a script that is going to loop millions of 
> times, building strings to build data and run for hours.  The next thing 
> you know, your cron job is using 450MB of memory and you try to figure 
> out what YOU did wrong.  Hours later you find this little jewel waiting 
> for you and realize you did not do anything wrong.  You just used the 
> language.

Yup, the language stole ~32Kb of your memory and used it to speedup the allocation of small chunks.

> Everyone ignored my last email about memory waste and large arrays.  I 
> can only assume that you will ignore this one too.  
> I am starting to see why Stefan became so bitter.

> I have always tried to squash the "myth" that putting variables inside 
> strings in PHP was bad, but now, I think I will flip on that.
 
> I tested as far back as PHP 4.3.9 and as new as 5.2.1.


-- 
Wbr, 
Antony Dovgal