Provide default services.yml, including APCu config

[danepowell]

On one of our ACE sites, we are seeing failing page loads with this error:
"Warning: apcu_store(): Unable to allocate memory for pool. in Drupal\Core\Cache\ApcuBackend->set() (line 177 of core/lib/Drupal/Core/Cache/ApcuBackend.php)."

According to support, this is due to Drupal 8 using APCu for some types of caching, which has a hardcoded memory limit that is too low.

The "strongly recommended" fix is to add the following to services.yml to tell Drupal to use the database instead of APCu for these types of caching:

services:
  cache.backend.chainedfast:
    class: Drupal\Core\Cache\ChainedFastBackendFactory
    arguments: ['@settings', 'cache.backend.database', 'cache.backend.database']
    calls:
      - [setContainer, ['@service_container']]

The long-term fix is to use Memcache, but memcache is not currently stable or recommended for D8.

Seems like Bolt should provide services.yml with this config by default.

We're testing this fix right now, and if it works will report back and try to open a PR.

[csedev]

Receiving the following error message after applying this change.

PHP Fatal error: Consistent cache backend and fast cache backend cannot use the same service.

What am I missing?

[geerlingguy]

I'm getting the same error now as @csedev, at least in local testing...

[csedev]

Acquia platform assigns a hard 8 MB limit to this cache backend, which is adequate for small cache pools, but was not meant to be used as a default cache backend. Unfortunately, Drupal 8 attempts to use APCu as a cache backend by default if possible.

In the meantime, I was able to avoid this issue altogether by telling Drupal not to use the APC user cache backend by default, instead relying on the MySQL database as a cache backend.

You can do this by adding the following line of code to your site's settings.php file:

$settings['cache']['default'] = 'cache.backend.database';

@geerlingguy @danepowell

[geerlingguy]

@grasmash - It seems the services.yml approach is preferred, at least according to Acquia support, but it wasn't working for me locally (see above referenced error)—should we recommend a settings.php change like @csedev used above, or work out the issue with services.yml?

[grasmash]

I suggest that we do what works for now and raise the issue with Acquia support regarding documentation of best practice.

[geerlingguy]

@grasmash - Thanks! Testing the settings.php fix now.

[Edit: It works!]

[bradjones1]

For anyone finding this in the future, the correct way to do this is documented at:

https://github.com/acquia/blt/blob/f0d02496371462c7fc0e64909789b10ded9c0cd5/settings/apcu_fix.yml

Also see https://www.drupal.org/node/2662844