快速，可扩展的哈希查找数据库（Berkeley'ish）

I use and love Berkeley but it seems to bog down once you get near a million or so entries, especially on the inserts. I've tried memcachedb which works but it's not being maintained so I'm worried of using it in production. Does anyone have any other similar solutions, basically I want to be able to do key lookups on a large(possibly distributed) dataset(40+ million).I use and love Berkeley but it seems to bog dow