It's a little bit hard to answer without more info but generally the ram disk isn't going to save your data unless you do something extra, so it's more useful for one-off tests or something where you need speed over permanence, like running unit tests (which it mentions in the readme). I don't use buildkit since I'm on windows but I do switch over to a ...
So, duh. I haven't totally figured out the problem - now I'm getting this -
SQLSTATE[HY000]  Connection refused
but the Access denied issue was a simple fix, i.e., use chmod.
See "How to Run MySQL as a Normal User" at https://dev.mysql.com/doc/refman/5.7/en/changing-mysql-user.html .
There's something wrong with your smart group with an ID of 95. However, this is unlikely to be causing a performance problem, since this query simply isn't running. If you can delete and recreate your smart group with an ID of 95, this error should go away.
Directly accessing the SQL tables is certainly possible, but not a recommended approach. Reporting (ie read only) is safer than attempting to write to the tables but there can be many tables to join correctly depending on what you are trying to do.
If the standard reports and the various reports extensions don't provide what you need, try getting your data ...