This is a followup of MDL-48228, where support of utf8mb4 was added to mysql/mariadb.

One of the differences is that, after the patch, new sites being installed from scratch get the dbcollation written to config.php, while that was not happening before (when everybody was utf8 and done). It has both ADVantages and PROblems:

1) ADV: 1-less query per request. Having the collation in config.php makes moodle trust it 100% and a minimum of one query (against slow information schema) is saved on each request.
2) PRO: In case of the dbcollation being changed (using our mysql_collation.php CLI, or any other strategy)... it's possible that the config.php becomes outdated and easily forget about t.

So this is about:

1) reconsider if we want to move new installations back to the initial proposal - aka, don't write the dbcollation to config.php ever, knowing it's 1-Q slower. That's exactly Adrian's patch. And it's how Moodle has been working since the born of the times.

2) if we decide to continue with dbcollation written in config.php.. then we need some check (enviromental or health) detecting if file and real collations diverge at any point.

And that's it. Would be interesting to have the outcome of this decided ASAP, so I'm raising its importance.

Also, abgreeve, would you please drag your patch from MDL-48228 here so everybody knows what we are talking about (getting rid of collation in config.php). TIA!

Ciao