PHP OPCache, Realpath Cache and Preloading

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Jachim Coudenys

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PHP-WVL

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Combell

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OPCache

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PHP Scripting Language Fire and forget No "manual" compilation

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Compilation PHP Code Lexing + Parsing: Tokens Compiling: Opcodes Executing

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https://engineering.facile.it/blog/eng/realpath-cache-is-it-all-php-opcache-s-fault/

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Throwaway language Always performs same steps All information is discarded Request per request

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OPCodes (usually) don't change

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Add in some cache! PHP Code Lexing + Parsing: Tokens Compiling: Opcodes Cache: Opcodes Executing

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Next run Cache: Opcodes Executing

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And the next run Cache: Opcodes Executing

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Even the next run Cache: Opcodes Executing

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OPCache Since PHP 5.5 Zend Optimizer "donated" by Zend

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Shared memory In computer hardware, shared memory refers to a (typically large) block of random access memory (RAM) that can be accessed by several different central processing units (CPUs) in a multiprocessor computer system.

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PHP-FPM Only "relevant" SAPI nowadays :) Master process Dynamic worker child processes Shared memory in the master

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Opcodes? In computing, an opcode (abbreviated from operation code) is the portion of a machine language instruction that specifies the operation to be performed.

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Vulcan Logic Dumper https://3v4l.org/A1B4H/vld#output

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This can get big quite quickly Libraries Frameworks

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OPCache Optimizer Gets better every release Optimizes: Branches Dead code ++$a vs $a++

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Interned strings Used in a lot of languages Since PHP 5.4 "Compression" for source code In shared memory (FPM master process)

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opcache_compile_file() opcache_get_configuration() opcache_get_status() opcache_invalidate() opcache_is_script_cached() opcache_reset() php.net/manual/en/ ref.opcache.php

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opcache.memory_consumption opcache.validate_timestamps opcache.revalidate_freq opcache.interned_strings_buffer opcache.max_accelerated_files (keys) opcache.max_wasted_percentage php.net/manual/en/ opcache.configuration.php

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Keys Full path to file Relative paths to files

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Wasted memory Opcache doesn't to "defragmentation" File changes cause recompilation opcache.max_wasted_percentage

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Opcache restarts OOM Restarts Hash Restarts Manual Restarts

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NEVER have a full cache!

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Opcache Priming opcache_compile_file() FPM Pools

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opcache.php demo

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APCu User Shared memory apc_* compatible

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Opcache File Cache Read opcodes from disk Can help busy sites Supports CLI (used to be "fire and forget") Cache to "user directory" http://talks.php.net/froscon15#/php7pcache1

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opcache.file_cache=/var/tmp/php/opcache opcache.file_cache_only=1 # Useful for CLI opcache.file_cache_consistency_checks=1 # Adler checksum

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Scenario's Memory Full? Interned Strings Full? Key store full?

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Deployment Strategies It Depends ¯\_( )_/¯

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Realpath Cache

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Realpath Cache Used to reduce IO Caches all possible paths to destination path explode('/') No shared memory (per worker process)! Mem*Workers 4M (Prior to PHP 7.0.16 and 7.1.2, the default was "16K")

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realpath_cache_get() realpath_cache_size () realpath() php.net/manual/en/ ref.filesystem.php

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realpath.php demo

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realpath_cache_size realpath_cache_ttl php.net/manual/en/ ini.core.php

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Preloading

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PHP has been using opcode caches for ages (APC, Turck MMCache, Zend OpCache). They achieve significant performance boost by ALMOST completely eliminating the overhead of PHP code recompilation. With an opcode cache, files are compiled once (on the first request that uses them), and are then stored in shared memory. All the following HTTP requests use the representation cached in shared memory.

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Preloading PHP 7.4 Part of opcache Starts in master process before anything else Loads code in memory "permanently" No need to copy from shared memory to process memory

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Preloading Opcache only works per file Preloading helps with class libraries Code will perform as internal entities (e.g. strlen, etc...) Simple file with autoloading magic

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opcache.preload https://wiki.php.net/rfc/preload#proposal

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PHP <= 7.3 PHP process starts up

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PHP <= 7.3 First request: app does new A() autoloader include 'A.php'; PHP "compiles" A.php into opcodes and stores it in opcache opcodes are executed

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PHP <= 7.3 Next requests: app does new A() autoloader include 'A.php'; A.php is already in opcache, no need to read the file and re-interpret the PHP opcodes are executed

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PHP >= 7.4 + preloading PHP process starts up

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PHP >= 7.4 + preloading preloading starts: preloader new A() preloader + PHP "compiles" A.php into opcodes and stores it in memory

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PHP >= 7.4 + preloading First request: app does new A() opcodes are executed

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PHP >= 7.4 + preloading Next requests: app does new A() opcodes are executed

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Normal vs Preloading first request we save calls to the autoloader + compilation to opcode + storing to opcache next requests we save calls to the autoloader + fetching from opcache

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https://externals.io/message/103333 https://wiki.php.net/rfc/preload https://github.com/php/php-src/pull/3538

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PHPArch Opcache article https://www.phparch.com/article/diving-in-the- opcache/

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Elastic Stack @ Combell Gather realpath/opcache/etc... data from all accounts Act upon that data (which is changing constantly) Autotuning

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Thank you! https://joind.in/event/php-wvl-may-meetup-at-studio- emma-2019/php-opcache-and-preloading