Checking on an old friend

1. MANOMANO
Preloading: a Post-Scriptum
Checking on an old friend

2. ManoMano confidential
The timeline
2018 2019 2020 😷 2021 2022
PHP RFC:
Preloading
Author: Dmitry Stogov
PHP 7.4 release Nothing to
report
Please disperse
Inheritance
cache released
in php 8.1
Author: see first block
Slides for talk
created
Author: yours truly

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Preloading of what?
(opcache) preloading
<?php
echo "hello world";
line #* E I O op fetch ext return operands
-------------------------------------------------------------------------------------
3 0 E > ECHO 'hello+world'
1 > RETURN 1
010001010100101001
101010100101000001
010110001001000111

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Why do we even need opcodes / bytecodes?

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How can I see the opcodes? 🔍
● Use 3v4l: https://3v4l.org/UIjRD/vld
● php -d opcache.enable_cli=1 -d
opcache.opt_debug_level=0x10000 hello_world.php
● phpdbg -p* hello_world.php
● php -d vld.active=1 hello_world.php
https://www.npopov.com/2017/04/14/PHP-7-Virtual-machine.html

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What happens when executing a PHP program?

7. Let’s accelerate! 🏎

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List of PHP Accelerators
● APC: bytecode cache (💀 since PHP 5.5) and user cache (split to
✨APCu✨)
● eAccelerator: 💀 since PHP 5.5, forked from Turck MMCache, 💀
since PHP 5.2
● ionCube: still alive, closed source, must pay 💰, main feature is
encryption
● XCache: 💀 since PHP 5.6
● Nusphere phpexpress: 💀 since PHP 5.4
● 👉 Zend OPCache: ✨alive and kicking✨
● Zend Platform: 💀 since PHP 5.2
● Windows Cache: 👽 works I suppose, but who cares?

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With opcache
but without preloading

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With opcache
but without preloading
For each and every file:

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With preloading
autoloading is bypassed *
* for preloaded symbols.
Otherwise, see previous slide
Since PHP 7.4

12. But wait, there’s more!

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Type dependencies resolution

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Type dependencies resolution

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Without preloading, this happens at runtime

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With preloading, this happens once, when starting
php-fpm
Only classes without unresolved parent, interfaces,
traits and constant values may be preloaded.

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With preloading, this happens once, when starting
php-fpm
PHP Warning: Can't preload unlinked class B: Class B cannot extend final class A in
/tmp/B.php on line 9
💥
To play with preloading in the CLI:
● opcache.preload=/tmp/preload.php
● opcache.enable_cli=On

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What should you put inside preload.php?
Symfony: let the framework decide, optionally fine tune it

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Caveats
The preload file has to exist before php-fpm starts! Make sure to do a cache
warmup!

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Caveats
Preloading is not per-pool, but php-fpm won’t complain if you try to
configure it per pool 😬

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How do I make sure it’s enabled?
● Use opcache_get_status()
● Check for preload_statistics

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Conclusion on preloading
● trade off
● needs work from
○ your SRE team
○ your framework
○ yourself of course
● hard to setup

23. Did I just waste your time?

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Inheritance cache

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Inheritance cache
Since PHP 8.1, without configuring anything

26. Send me your benchmarks 🙏
🐘 @greg0ire@phpc.social
🐦 @greg0ire