google app engine - Spatial Search Objectify, appengine -

i want use, objectify spatial search. have entities have longitude , latitude associated them. latitude , longitude information dynamic e.g. service providers (like electrician, carpenter) in city. want implement query gives me service providers providing specific service in 1 km radius. searching on google reveals following options

1. use objectify geohashes - not sure, how accurate , scalable solution is
2. use google search - need entities(or part of it) duplicated in form of documents , able support dynamically updated locations.
3. use other database mongodb

assuming few millions entities , latitude/longitude dynamically updated, please suggest me appropriate option.

thanks ittium

i've used geohashes. works, although end selecting more data exact bounds looking , filtering out extra. might or might not solution depending on specific application. requires writing more code has fewer moving parts (all in datastore).

google search , "other database" same architectural pattern - use task queue replicate updates external index. if want quick solution, search service easiest wrap head around.

just pick 1 solution , run while. can reindex data different solution.