One of the best optimizations I have done was switch my caching from using a key-value serialization to an array form. I'm caching fairly large data reports about computer performance. It brought the average cache size from 100 megs to around 4 megs.
This is why I can't consider databases like RethinkDB or Mongo. They are taking such a big hit already for using something like BSON as a storage that I don't even want to be involved in that train of thought anymore.
[{'first_name':'mike'},{'first_name':bill'},...]
vs
{meta: {'header':['first_name']]}, data: [['mike'],['bill],...]};
This is why I can't consider databases like RethinkDB or Mongo. They are taking such a big hit already for using something like BSON as a storage that I don't even want to be involved in that train of thought anymore.