On Wed, October 25, 2006 11:58 am, jeff.phplist@xxxxxxxxxxxx wrote:
> Are the include files only compiled when execution hits them, or are
> all
> include files compiled when the script is first compiled, which would
> mean a cascade through all statically linked include files. By
> statically linked files I mean ones like "include ('bob.php')" - i.e
> the
> filename isn't in a variable.
As far as I know, the files are only loaded as execution hits them.
If your code contains:
<?php
if (0){
require 'foo.inc';
}
?>
Then foo.inc will never ever be read from the hard drive.
You realize you could have tested this in less time than it took you
to post, right?.
:-)
> Are included files ever unloaded? For instance if I had 3 include
> files
> and no loops, once execution had passed from the first include file to
> the second, the engine might be able to unload the first file. Or at
> least the code, if not the data.
I doubt that the code is unloaded -- What if you called a function
from the first file while you were in the second?
> Thirdly, I understand that when a request arrives, the script it
> requests is compiled before execution. Now suppose a second request
> arrives for the same script, from a different requester, am I right in
> assuming that the uncompiled form is loaded? I.e the script is
> tokenized
> for each request, and the compiled version is not loaded unless you
> have
> engine level caching installed - e.g. MMCache or Zend Optimiser.
You are correct.
The Caching systems such as Zend Cache (not the Optimizer), MMCache,
APC, etc are expressly designed to store the tokenized version of the
PHP script to be executed.
Note that their REAL performance savings is actually in loading from
the hard drive into RAM, not actually the PHP tokenization.
Skipping a hard drive seek and read is probably at least 95% of the
savings, even in the longest real-world scripts.
The tokenizer/compiler thingie is basically easy chump change they
didn't want to leave on the table, rather than the bulk of the
performance "win".
I'm sure somebody out there has perfectly reasonable million-line PHP
script for a valid reason that the tokenization is more than 5% of the
savings, but that's going to be a real rarity.
> Fourthly, am I right in understanding that scripts do NOT share
> memory,
> even for the portions that are simply instructions? That is, when the
> second request arrives, the script is loaded again in full. (As
> opposed
> to each request sharing the executed/compiled code, but holding data
> separately.)
Yes, without a cache, each HTTP request will load a "different" script.
> Fifthly, if a script takes 4MB, given point 4, does the webserver
> demand
> 8MB if it is simultaneously servicing 2 requests?
If you have a PHP script that is 4M in length, you've done something
horribly wrong. :-)
Of course, if it loads a 4M image file, then, yes, 2 at once needs 8M
etc.
> Lastly, are there differences in these behaviors for PHP4 and PHP5?
I doubt it.
I think APC is maybe going to be installed by default in PHP6 or
something like that, but I dunno if it will be "on" by default or
not...
At any rate, not from 4 to 5.
Note that if you NEED a monster body of code to be resident, you can
prototype it in simple PHP, port it to C, and have it be a PHP
extension.
This should be relatively easy to do, if you plan fairly carefully.
If a village idiot like me can write a PHP extension (albeit a
dirt-simple one) then anybody can. :-)
--
Some people have a "gift" link here.
Know what I want?
I want you to buy a CD from some starving artist.
http://cdbaby.com/browse/from/lynch
Yeah, I get a buck. So?
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