I debated going that route, but the OpenWorker allocates block_cache and filter_policy as well. The filter policy can be created in the DB constructor, but block_cache's size depends on params passed to OpenWorker.

Most importantly, I wasn't sure if leveldb was allowed to munge stuff in options. I saw lines in leveldb starting with `options.block_cache = ...`. Looking more closely, I see now that leveldb only messes with those attributes if leveldb allocated them.