I take my last comment back. While the patch appeared to be working for about a week or so, I am suddenly seeing the following error even though the service and FactoryInterface are present in the codebase:
You have requested a non-existent service "cache.backend.memcache_transaction_aware".
Is there a specific place the `cache.backend.memcache_transaction_aware` needs to be defined? I have the following in my in docroot/sites/settings/global.settings.php:
$settings['cache']['default'] = 'cache.backend.memcache_transaction_aware';
Like I said, it was working for about a week, but with a recent deployment that changed the code to a branch without the patch, now when we switch the code back to the branch with the patch (and settings) we are getting the above error.
Is there someplace else the new service needs to be explicitly defined/injected?
Memcache module is enabled and I can see the new cache.backend.memcache_transaction_aware service in memcache.services.yml
But for some reason, even after a cache rebuild, Drupal is saying the service isn't defined.
Could opcache be to blame?
I can confirm that patch #45 appears to have solved the issue of stale content for a site using considerable nested entities (paragraphs), using cache.backend.memcache as their default backend and where a node edit form might take 10 seconds or more to submit while the node being edited is receiving traffic.
To reproduce the issue I developed a simple JMeter test to request the test page as an anonymous user with a cachebusing query string. The test runs with 10 concurrent users.
While the load test is running, I manually edit the test page, which contains paragraphs. I edit one of the paragraph components and update the title and kicker fields. I submit the node edit form.
Prior to the patch, the node edit form would submit, but the embedded paragraph form fields that were updated do not appear on page load AND/OR when reloading the node edit page. It seems as though the race condition of a simultaneous anonymouse user request for the page has memcache get the old/stale values before they can be deleted and populated with the new values.
After applying the patch and changing the default cache backend from cache.backend.memcache to cache.backend.memcache_transaction_aware, and clearing Drupal and Varnish cache, I repeated my reproducible steps.
With the patch applied, I immediately saw the new values for both fields as both an authenticated and anonymous user. Reloading the node edit form also showed the updated values.
I went through the reproducible steps 3 times, and all 3 times the new values were displaying, which leads me to believe this patch (#45) is working as expected!
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