The reason to split it is that as soon as you give your BI dept. free reign to query the tables for users, user_widgets, widgets, widget_metrics, widget_metrics_metadata, and half a dozen other things with one query, they will do it and lock up your production database by running some atrocious 12 hour query composed completely of select * from window_functions that you’ll be back at square one in no time.
The other (more serious) problem is that if multiple services can edit the same data independently, eventually they will, and it will cause data loss or degradation that will be catastrophic. And, although you CAN isolate things with permissions, the chances of this reliably getting done without a lot of time put into DBA (a role which simply doesn’t exist at startups), is very low in my experience.
The other (more serious) problem is that if multiple services can edit the same data independently, eventually they will, and it will cause data loss or degradation that will be catastrophic. And, although you CAN isolate things with permissions, the chances of this reliably getting done without a lot of time put into DBA (a role which simply doesn’t exist at startups), is very low in my experience.