Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:990
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Date: Mon, 21 Apr 2003 12:56:07 +0200 (CEST)
To: Vegard Munthe <vegard@copyleft.no>
cc: PHP Developers Mailing List <internals@lists.php.net>
In-Reply-To: <20030421124532.F86580-100000@unity.copyleft.no>
Message-ID: <Pine.LNX.4.53.0304211249370.20318@jdi.jdimedia.nl>
References: <20030421124532.F86580-100000@unity.copyleft.no>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Subject: Re: [PHP-DEV] Memory.
From: derick@php.net (Derick Rethans)

On Mon, 21 Apr 2003, Vegard Munthe wrote:

> I've asked these questions a number of other places. It seems no-one
> really knows. So, even if this might not be the right list for these
> questions, I hope someone can bare with me and help answer a few
> questions, or direct me to someone or some doc that can.
> 
> Questions:
> 
> 1) Since there are no functions to tell the memory usage of variables and
>    objects, is there a way to calculate memory usage of variables and
>    objects?

No, there is none. But there will be a function to show the total memory
usage in PHP 5 : memory_get_usage().

> 
> 2) When a script loads different files as includes, does it take from the
>    memory_limit pool of memory?

Yes

> 
> 3) When leaving a function, are variables in the function's scope
>    freed? I.e. is the memory used by a function completely freed for
>    the rest of the script to reuse?

It's returned for the rest of the script to reuse, BUT there will always 
be an allocated pool that will not be freed.

> 
> 4) Is there any way to free memory used within a script? Does for
>    instance $var = ""; free the memory previously used by $var?

Only a bit, doing $var = NULL will free the string contents, but not the 
variable container itself.

> 
> 5) Is it not aa good idea to use objects if you plan to collect thousends
>    of them in PHP? Do they for some reason take up substantially more
>    memory than other variables?

They do use quite a lot more memory then arrays, it just depends a 
little on how they are distributed, and which variables you see in mind 
for the relacement of objects.

As a final word you might want to checkout Xdebug
(http://xdebug.derickrethans.nl) which has a trace function
(xdebug_start_trace and xdebug_dump_function_trace) to see how much
memory a script uses per function call. (You will need to compile PHP
with the --enable-memory-limit option for this to work though).

Derick

-- 
                                        "my other box is your windows PC"
-------------------------------------------------------------------------
 Derick Rethans                                 http://derickrethans.nl/ 
 PHP Magazine - PHP Magazine for Professionals       http://php-mag.net/
-------------------------------------------------------------------------