It's always tempting to build it yourself. Initially we built our own data store too, partly because it was a great geek challenge, and then went back to InnoDB and NoSQL solutions once we figured we can't compete with 1000's of open source devs and battle hardened products.

Our hardware bill for our entire server cluster, which we own, is only slightly more than Druid's monthly cloud bill. [My company is the largest real-time analytics provider on the web]

Few people realize that Redis was created by Salvatore to provide a real-time analytics product - and then it grew into so much more. Also InnoDB's clustered indexes are spectacular when it comes to answering questions like the one's the OP has posed.