Limit number of requested points from the database

[shaardie]

We have a lot of data in our database and currently no mechanism to limit the maximal number of requested points from the database, which makes it pretty easy to overload our service.

This does not have to be on purpose. It could simply happen by accident.

Limiting the number of geo.jon points is pretty straight forward, but limiting the number of data points involved in calculations in average.json and statistics.json is more complicated.

My approach would be the following:

We can calculate the average density d of the points we have per day. Then for every request we get a polygon p and a timespan t from the user.

So we can estimate the number of involved points with d*p.area*t.

With this estimation we can directly stop the query with a proper error message.