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some background to the questions

I have just been browsing through some *.php files used in the moodle CMS. Moodle uses PHP-Scripts to generate content of HTML-pages send to the visitors dynamically. Often something like this happens ("inclusion cascade"):

// file: file1.php
require(file2.php);

and 

// file: file2.php
require(file3.php);
require(file4.php);

etc...

Indeed starting from the requested *.php file until finally producing some output there is quite a cascade of inclusions of other files necessary. Even if this makes much sense it worries me for the reason of its impact on speed/performance. It seems that each time a lot of initialization is redone.

The question

Knowing that the HTTP protocol a stateless protocol, it would appear to me that for each request that is sent to the server, it is necessary to run through all possible initialisations done in the PHP/CGI code over and over again. Is this a valid/true assumption?

Example: I have a need to access a database and this I want to do safely using some objects that help with doing all this "safer" prepare statements/sanitizing etc. The object used for this is hence created in a file I include ( i.e. myDatabaseAccessObject.php).

With regard to the example the question is:
whether it is true, that due to the nature of HTTP being stateless, that there is no chance to keep the work of setting up (i.e parsing) the myDatabaseAccessObject.php from being done all over again upon each request?

Or does PHP over a way to cache the work already done? (if so, is done in a transparent way (i.e. the script-author can tell what to cache) or obscured way, the php-engine does some caching not visible do the author?)

Is it that I have a absolutely flawed perception of what is going on, or is indeed work done over and over again, which could be saved if some initialization necessary for the PHP-Script would have been saved between multiple subsequent requests?

humanityANDpeace
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  • Just a sidenote, per my experience moodle performance is really bad. – DevZer0 Sep 02 '13 at 08:35
  • Just for a laugh, try writing hello world in zend framework. – Nick Maroulis Sep 02 '13 at 08:40
  • a lot of it, in a lot of cases, is just done each and every time, no problem on any piece of modern hardware, but theses are gross generalisations. –  Sep 02 '13 at 08:40
  • @marabutt: `$vim index.php` line 1: `exit('hello world');` the (pre-dispatch-) the app needn't be bootstrapped. For a cry: try doing the same with Java – Elias Van Ootegem Sep 02 '13 at 08:51

2 Answers2

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You are completely right. All database connections en other initializations are done on every PHP script execution. It is exactly because of the statelessness of the HTTP protocol.

That being said, there are ways to speed up the process. There is the PHP session handling that can do stuff for you (although it can't cache connections), Smarty for example has a decent caching and compiling system, etc.

Bart Friederichs
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  • smarty is a templating system, you're not suggesting using it for db connections, are you? – Elias Van Ootegem Sep 02 '13 at 08:52
  • @EliasVanOotegem no. My point was that it compiles and caches, so there is less processing overhead on each page request. Database connections are only a part of the page request. – Bart Friederichs Sep 02 '13 at 09:05
  • What kind of stuff would the **PHP session handling** be able to do for us? I have used it like most people mainly for keeping the track of a logged in user (i.e. so that users need not authenticate over and over again at each step). I will read through the link, but just for kick (you might know): Will the said handling be able to avoid reinicialisation of a big share of code (i.e. reparsing of the cascades?) – humanityANDpeace Sep 02 '13 at 09:53
  • @humanityANDpeace without knowing what happens in the cascaded initialisation, you could think of keeping cached data without the need of going to a database. Of course, the whole "performance" thing is way bigger and complex than just using sessions or cached templates. – Bart Friederichs Sep 02 '13 at 10:39
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Well, to kick off: HTTP isn't really stateless anymore. HTTP 1.1 added persistent connections, which, in itself doesn't make it stateful, but doesn't make the protocol entirely stateless as such. If HTTP 1.1 were to be truly state-less, and you would use persistent connections (chunked transfers), you'd curse the protocol for being too slow, so they've worked around it in a way, that's why I've heard HTTP 1.1 being referred to as dirty-stateless. That's the point I was getting at.

So, back to your question: Yes, a standard installation of PHP/CGI (sure you're not using fCGI?) will have to parse, compile and execute all the code for each request. It's not that big of a deal, but it's overhead nonetheless.
You can't hold states in between 2 requests, not really. This, if you come to think of it, is why many deem the static keyword rather pointless in PHP, but that's a different matter.

Your question focusses on a db connection. Well, you can use persistent DB connections, and PHP might draw the next connection from a connection-pool. But that's dangerous, messy and just an accident waiting to happen.
Conecting to a DB isn't likely to be the major bottleneck in your case. Since you're using moodle, I'd say that's going to be excessive I/O operatrions (the require-cascade of which you speak).

This can, quite easily, be avoided by caching the actual bytecode, that PHP generates when compiling your scripts. Look into APC, AFAIK, it's the most popular caching extension in use. It gives you control over what is cached, how and when...
If you like to live on the edge, and you're not working on something critical, you could even check to see how much performance gain you'd get if you compile your code to an executable

Elias Van Ootegem
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  • Great!, many thanks for giving confirmation about that in principle it is not out of the question that reparsing etc. etc. would happen. It is also quite nice that you brought some references to how to cache and even compile (which might hence be cooler, even). Have to give this a look. – humanityANDpeace Sep 02 '13 at 09:55
  • @humanityANDpeace: Don't expect miracles from compiling PHP code, though... facebook tried to X-compile PHP to C++, and run the C++ compiled bins on their server. True enough, the compilation step of PHP could be skipped, so it reduced the server-load, but nowadays, the HipHop compiler also uses bytecode compilation, because hiphop was _slow_ – Elias Van Ootegem Sep 02 '13 at 10:05