execute a database management research project that is of interest to you. Here are some topics that I’ve thought of:

Security (this is my forte, so, if you choose this I can be quite helpful.)
Availability (how do you design and implement a database system that is always reachable and “performant”, despite network outages, zero-day attacks, hardware failures, software bugs, etc.)
Performance (what do you measure, how do you measure it, how do you structure your database to “optimize” performance.)
Disaster Recovery (Fires, earthquakes, corona virus…)
Migration (how do you migrate a legacy data set to a modern “platform”. Beware: this is a hard topic.)