MemcacheD with persistent connections

Thanks for the patch ndobromirov, it works good on our setup and we see a small increase in performance. I added a section for redistributing keys when the users uses Libketama and there is an error when setting a key because one of the memcached server is unavailable.

Regarding the #2 comment about MemcacheDriverFactory::flush() - I found this method is only run when the statistics output is requested by the MemcacheAdminSubscriber - When that stats option is disabled, during regular usage, the flush is never called. We can also see via netstat that the connection count is stabilised.

I did a test of #6 and it worked fine. My benchmark showed that the site was around 25% faster (local db and memcached).

I re-rolled the patch to not include the changes in info.yml. No other changes where made

Tested #11, applied fine.

FILE: /memcache/src/Connection/MemcachedConnection.php
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
65 | ERROR | [x] Doc comment long description must end with a full
| | stop
----------------------------------------------------------------------
PHPCBF CAN FIX THE 1 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

FILE: /memcache/src/Driver/MemcachedDriver.php
----------------------------------------------------------------------
FOUND 1 ERROR AFFECTING 1 LINE
----------------------------------------------------------------------
26 | ERROR | If the line declaring an array spans longer than 80
| | characters, each element should be broken into its own
| | line
----------------------------------------------------------------------

Time: 119ms; Memory: 8MB

Some code style issues still, and created an interdiff without the info file update because the #6 would not apply against the latest dev version. ( Only difference remains is a moved method ) So code is good, but we need some minder codestyle fixes.

Fixing codestyle errors.

I'm not really sure if this works or not but one way seems to be to call isPersistent() method on the Memcached() object.

I thought why not have it on the /admin/reports/memcache next to connections:

Is it ok that the "Connections 6 open of 1 104 total" is still growing? On our dev server 1104 is 16 000.

Patch #17 works for me. Fine!

Maybe you can choose $settings['memcache']['key_prefix']; as $settings['memcache']['persistent'] per default? In shared environment it could be great to have a pconnection for each drupal. Maybe this could be a hint in the README.

Thank you for your work.

You have to be aware of the fact that the design hypotheses of libmemcached (on which the memcached extension is built) are not entirely compatible with PHP, and as a consequence, the behavior of any code using the memcached extension with persistent connections is often unexpected in the presence of server errors, which can lead to the feeling that bugs exist in memcached servers / libmemcached / the memcached extension / this module, while the underlying issue is in fact a hardly documented design choice regarding expectations of behaviour in the face of errors.

I do not have the link at hand, but IIRC there were already a couple of tickets around these issues. The summary being: avoid using the memcached extension and stick with the memcache extension, which is tailor-made for the PHP design choices and behaves as you would expect in the face of errors.

Also, since the memcache extension has been working quite nicely with PHP 8 since 2020 and version 8 of the extension, and features are almost never critical anyway, downgrading from critical to normal

Changed ReadMe.txt to ReadMe.md

This needs a bit more tweaking than I thought. Will try to get revision up tomorrow. It appeared to be working on my machine but evidently it is not.

Posting the static patch because using the MR doesn't allow pinning to a specific commit, so anyone can submit pretty much anything and inject it into our codebase IIRC. This also fixed our issue.

The md5 in the constructor gives a deprecation warning as the $base_url can be NULL;

Changing the patch so and empty base url is set to an empty string in the md5()
Interdiff with patch 18 of comment #25
```
- $this->persistentId = $settings->get('persistent_id') ?? $settings->get('key_prefix') ?? md5($base_url);
+ $this->persistentId = $settings->get('persistent_id') ?? $settings->get('key_prefix') ?? md5($base_url ?? '');
```