Graylog and elasticsearch might fit on that, depending on how much is already used, and if you set the heap sizes at their bare minimum… but it will perform badly, and it’s overkill anyway if you just need this simple stat.
I would look into writing a custom log parser for goaccess (goaccess.io/man#custom-log) and let it parse your bridge logs. This is how the geolocation section looks in the HTML report (each continent can be expanded and it will reveal the stat by country).