RFC: feat(functions): PHP 7.4 preloading

[bshaffer]

WIP for preloading in PHP 7.4 Cloud Functions

This demo suggests the users do the following:

1. Add the following to composer.json

   {
       "config": {
           "optimize-autoloader": true
       },
   }

2. Add a preload.php file containing the following:

   require_once __DIR__ . '/vendor/autoload.php';
   
   // By running "composer dump-autoload --optimize", the classmap file contains a
   // mapping of optimized class files.
   $composerClassmap = __DIR__ . '/vendor/composer/autoload_classmap.php';
   
   $classesToPreload = require $composerClassmap;
   
   foreach ($classesToPreload as $class => $file) {
       require_once $file;
   }

3. Add a php.ini containing the following:

   opcache.preload=preload.php

And that's it! Preloading will work for any/all classes handled by Composer's autoloader

[snippet-bot]

Here is the summary of changes.

You are about to add 1 region tag.

• functions/tips_preload/index.php:18, tag functions_tips_preload

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[bshaffer]

I am was receiving the following error when running the deployment:

PHP Fatal error:  Uncaught Error: Class 'PHPUnit\Framework\TestCase' not found in /workspace/test/IntegrationTest.php:28
Stack trace:
#0 /workspace/preload.php(12): require_once()
#1 {main}
  thrown in /workspace/test/IntegrationTest.php on line 28 

This is very strange, since test/IntegrationTest.php does not show up (locally) when I run the same composer commands. I tried ignoring test/ via .gcloudignore, and the error changed to Failed opening required '/workspace/test/IntegrationTest.php', which isn't any better.

To fix this, I deployed with a new function NAME. I believe the reason is the vendor directory is cached for multiple deployments with the same function name if composer.json has not changed. So this is important to note...

I believe the main fix here is to upgrade the server's version of composer. The newer versions will skip adding classes to the classmap if they do not conform to the autoloading rules inside composer.json, allowing test classes and other dev classes to be deployed to the server without throwing errors like this.

[grayside]

Do we have any data on the benefits? E.g., A/B performance?

[bshaffer]

@grayside no benchmarks, no, but we should definitely do some sanity-checking here. In theory, it should provide significant improvements on all requests, as the entire classmap is loaded into memory before the first request.

[vishwarajanand]

Closing since we are not actively tracking this work. Maybe we'll want to come back to this if optimize flag proves optimistic.

[bshaffer]

This is frustrating, since a lot of work was done to add this sample which could help the performance of Cloud Functions for a lot of our users. Maybe @grayside could suggest someone that might want to pick this up and add it to our docs?

[rogerthatdev]

Verified that this is deployable via the following:

gcloud functions deploy php-http-function-w-preload --gen2 --runtime=php74 --region=us-central1 --source=. --entry-point=preloadDemo --trigger-http --allow-unauthenticated