A lot of these AppEngine costs too much notices have been coming up recently, but upon further inspection, they all tend to boil down to operator error.

Unfortunately, AppEngine isn't forgiving of that and there is a real monetary value associated with questionable engineering design. Or, design that wasn't thought through enough in the context of a service like AppEngine.

This leads to a few people getting upset and making a lot of noise when the reality is that AppEngine is actually an amazing service.

So, to boil down the operator error from a quote in the thread:

"We're running a mapreduce to change the geobox sizes/precision for a large number of entities."

That is the real source of the problem. Instead of using geoboxes, they should be using geohashes, which allow arbitrary precision.

http://code.google.com/apis/maps/articles/geospatial.html http://en.wikipedia.org/wiki/Geohash

Instead of an indexed property that looks like this (what they currently have):

[u'37.3411|-121.8940|37.3395|-121.8926', u'37.3411|-121.8929|37.3395|-121.8916', ...]

They would have an indexed List<String> property that looks like this:

[8, 8f, 8f1, 8f12, 8f12a, 8f12ac, 8f12ac6, 8f12ac60, 8f12ac605, 8f12ac605f, 8f12ac605fb, 8f12ac605fb3, 8f12ac605fb34]

Finding if the location is in a box would be computing the hash from the lat/lng (there is free code out there to do that) and then doing an indexed 'in' query. The indexes would only need to be updated if the location of the entity changes, not when they want varying levels of precision.