I recently right-sized the data and log files for an RDS database, leaving just a few GB of unallocated space. Shortly thereafter, something allocated, then deallocated, 1 GB of the margin of error. What might have caused this?
All of the databases - including tempdb - are either tiny (MB) or at exactly the size they've been set; they add up to 197 GB, leaving 3 GB free on a 200 GB instance. And yet:
Clearly, if this happens again in a slightly greater magnitude, there will be a problem. For now, I can simply shrink one of the database files to give a larger margin, but I'd like to understand what actually happened.