With D8 I would love to see some cold hard stats benchmarks comparing mysql and mongodb storage backends for various profiles, eg vanilla D8, D8 with x content types and x nodes, or Drupal Commerce and Drupal Commons installs.
I have read some benchmarks on other mysql and mongodb projects, and I became uncertain if mongodb is really all that necessary.
I have read in many comparisons
- https://www.google.de/webhp?q=mongodb%20vs%20mysql#q=mongodb+vs+mysql
- http://stackoverflow.com/questions/9702643/mysql-vs-mongodb-1000-reads
- http://www.sarahmei.com/blog/2013/11/11/why-you-should-never-use-mongodb/
that you cannot really do such thing as its nosql vs relational, apples and oranges bla bla bla. But, after all, stats matter as well and in our case we have a clear target that is Drupal 8.
In D6 and D7, Drupal with Boost allowed serving simple cached HTML content on the fly and proved unbeatable when it came to performance (Also eliminated most of Drupal as a bottleneck)
Also, posted this question as an issue at https://www.drupal.org/node/2367565