It’s unfortunate that the writing style wasn’t up to par, but I want to point out that I read the entire article and it doesn’t contain any criticisms of Redis. From the sounds of it, Redis worked perfectly and achieved what they wanted, which was beyond the capabilities of a simple MySQL implementation of the system.

In the end, they found a way to make it all work on MySQL, which solved some of the inherent complexity of using multiple databases side by side (but again this isn’t a criticism of Redis, the same problem would exist for any pair of databases).