Added caching support to geohash_filter

[bleskes]

No description provided.

[s1monw]

I don't think we should cache this by default. It's very unlikely that you have cache hits here. In-fact this filter should rather not be cached at all and never be turned into a big bitset since this fitlter is likely going to be very fast (it's really just 9 terms after all?) I am not sure if we should do this?

[jpountz]

+1 to add the ability to cache it
-1 to cache it by default

[bleskes]

I'm a bit on the fence regarding the default - I was triggered to add it by someone using the geohash_cell filter as the fastest way to limit the result to a certain area. They were using level 4 with neighbours which translates to 120KM by 60KM box and put it under a bool filter which causes it to generate a bit set anyway. Maybe cache by default on level 4 or up?

I don't have a good grip on the different usages of the geohash_cell filter, so if the people fill it shouldn't be cached, I'm good with that. Let me know.

[s1monw]

yeah I'd let the user decide ie. follow @jpountz suggestions.

[bleskes]

kk. Pushed another commit with the cache turned off + added cache/cachekey params to the java builder.

[bleskes]

@s1monw pushed another commit with an extra test

[s1monw]

LGTM ;)

[bleskes]

merged. Thx @s1monw , @jpountz