When should you use files instead of MySQL for speed?

Question

MySQL

Databases fall on shared hosting or are very often not optimized.
here they write about the speed of files and muscle habrahabr.ru/post/230393 :

Files
When all the ways to optimize MySQL were tried, I decided to write the morphological dictionary to a file and search it with a binary search. The results exceeded my expectations. The speed has tripled.

In this regard, the question is: what situations did you have when you need to use a faster way to access information?

Answer 1

Why the files are here is not clear, with such a volume of data it is easier to stuff everything into RAM into a hash and that's it.
Situations when we pump out part of the data into memory and build hashes constantly arise during any unloading and indexing.

Answer 2

Never. For speed, you need to use Redis / Memcache, etc.

Answer 3

Isn't it obvious? Any accelerations need to be applied when the speed of the database is not enough.