Exactly. We created our own even store on top of a SQL database. It's quite simple to do, and it is blazing fast because it is custom built for our use case. It's an append log of every event, their time, their type, and some other info about them (account, user, etc.). The event itself is stored as json, and we can just use Json functions of SQL Server to query those for diagnosis if need be. We've also got failure reporting built in, and strict referential integrity for various other tables to link into the main event storage table.

It was actually a pretty fun weekend project.