Memory savings...passing function data byRef?

s_shrum

Is there any memory savings by passing data back from a function ByRef versus a standard return?

The reason I ask is that my script is now dealing with larger datasets and I'm starting to get PHP's 8 meg barrier error.

I've gone through and UNSET any large varaibles that the script held that were no longer needed and that seemed to help a bit (didn't see the error as much).

I guess I'm looking for a beginners guide to PHP memory optimization.

TIA

rebelo

Implemented on a large scale, I assume this would help somewhat with your problem. As it is currently, you're making copies of every variable when you pass them to functions normally (essentially doubling the memory usage if you're doing enough of it). Passing by reference will just make a placeholder which points to the same location of memory.

toplay

FYI - you can increase memory usage using ini_set() too:

http://us3.php.net/manual/en/ini.core.php#ini.memory-limit

http://us3.php.net/manual/en/function.memory-get-usage.php

rebelo

While you can certainly do that, I personally think that if your web script is consuming more than 8MB of memory, you should probably be taking a look at your coding style and thinking about optimizations you can do. I've been involved in some pretty large PHP/MySQL web applications in the past and have only ever hit this error when I've made a code mistake of some sort.

toplay

rebelo wrote:
While you can certainly do that, I personally think that if your web script is consuming more than 8MB of memory, you should probably be taking a look at your coding style and thinking about optimizations you can do. I've been involved in some pretty large PHP/MySQL web applications in the past and have only ever hit this error when I've made a code mistake of some sort.

I totally agree. I was just giving s_shrum info about the setting in the php.ini file.

FYI:
http://us3.php.net/manual/en/language.references.php

hth.

s_shrum

I put in some memory usage lines in my code and here is what I got back:

1: 6043672 - START

2: 6047248 - PRE PARAMS

3: 6053888 - POST PARAMS

4: 6053920 - PRE TEMPLATES

5: 6107952 - POST NESTING

6: 6082096 - POST TEMPLATES / PRE PLUGIN

7: 6374288 - POST PLUGIN

8: 6374360 - PRE ORDER

9: 6375504 - POST ORDER / PRE WHERE

10: 6375992 - POST WHERE / PRE SEARCH

11: 6375992 - POST SEARCH / PRE SLICE

12: 6376144 - POST SLICE / PRE RESULTS

13: 7038872 - POST RESULTS / PRE NEST


Fatal error:  Allowed memory size of 8388608 bytes exhausted (tried to allocate 660505 bytes) in /data/webs/shrum.net/html/cats.php on line 322

I've noticed that my Start value either is around 6 meg or 2 meg...I can't figure that out either.

Overall I'm generating about a meg of data each time (if I'm reading this right) so I'm stumped as to why I'm maxing the mem out.

Any ideas?

TIA

s_shrum

I put in some mem reporting using the info you gave.

I'm seeing something strange...Sometimes my starting memory is 2 megs...other times its 6 megs...other times its 8 megs.

The data that the script is creating is about a meg at most.

Is the memory space for PHP a collection of all the visitors at my site accessing the script at around the same time? ALA:

1 user = 1 megs
2 users = 2 megs
...

???

On another note, is it nessecary to unset variables at the end of a script run to free up memory or does PHP take care of this quickly?

toplay

No. It's for that particular script execution.

PHP will free up the memory at the end of the scripts execution.

I can't help much without seeing the code.

Drakla

With respect to passing and returning by reference, because of the internal reference counting mechanism the script will only actually create copies when modifications to items occur. E.g

// imagine we have a class Foo

$var1 = &new Foo();
$var1->name = 'Spanner';

$var2 = $var1;    // there's still only one object Foo with a reference count of 2

$var2->name = 'Muppet';   // a copy is now made and updated

The same thing occurs when you pass data back from a function, the receiving variable really just increases the reference count to the data - but when the function goes out of scope the reference count to the item returned drops and is now just coming from the object it was assigned to ($item = func_data()) so in reality returning by reference isn't necessary for most functions, only functions that expressly deal with returning references for other purposes.

That all sounds a bit muddy as I read it back, but it's all in the manual somewhere.