hey @littleberk, all datastores rely on indexes to optimize the lookup of rows in the critical path of the application, which is necessary in order to achieve low latency. You can try with other datastores, I'd suggest CockroachDB, but I'm not sure it's going to be entirely different.
That does not mean that the current setup with our indexes is absolutely optimal, I'm sure there are still things we could look into, but I have to say we were looking into covering indexes, which will be even heavier.
I think @Jake has done some load-tests but I'm not sure we measured the size on disk.