What i did / Steps to reproduce

When my world finished rendering, the table size on my DB was about 3GB or so (doesnt matter exactly, but around that ballpark).

Expected result

File (DB) size stays the same save for tiny deviations if blocks are added (I have a worldborder well within the rendered area, so no new chunks could be saved)

Actual result

File (DB) size kept creeping up over time, now (same world!) reaching 15GB

Context

5.9 Paper, using SQL storage

BlueMap doesn't save any history-data. If a tile gets rendered the old map-tile always gets overwritten on the database.
My guess would be that your database still growing is due to something else, e.g. your database software itself caching something or generating indexes. But nothing that BlueMap can control. Please check your database's manual..

If you still think it's bluemap's fault, please monitor the line-count of your tables and tell me which table is growing exactly. Also tell me which database you are using exactly.
I will then reopen this issue :)