mongodb? MySQL? PostgreSQL?
If someone would add pluses and minus, let me know.
Why I ask:
I am a mobile startup. I need a database that supports spatial indexes. The spatial index must be able to do something more sophisticated than simply asking whether a point is in a rectangle. For that one, I do not think we need spatial indexes at all.
At the least I need to be able to find the 20 closest points to a certain location.
Yes, I can put a small rectangle, see if 20 points are there, then make a bigger rectangle. That's reasonable, but I want something simpler and faster.
Basically I just see what other successful startups use and follow. Many recommend mongodb.