How does Scuba differ from Presto which is also developed by Facebook? It seems that it stores data in-memory and have data expiration feature but also has many common features such as SQL and distributed processing.
As @ot said, Presto is just a query engine and it doesn't provide a backend. It provides an API that allows it to be plug in to different data warehousing systems. I would assume functionality depends to some extent on what your data is stored in, but in general Presto supports the full suite of standard relational db style queries.
Source: I work at FB as well. In fact I was using Scuba just now to do a quick analysis of our storage requirements for Scuba itself :)
This was the reasoning behind a very key architectural decision at Interana that makes it different than Scuba - instead of developing an in memory system, Interana created a custom data store that is heavily optimized around using spinning disk and CPU cache. This makes it incredibly fast and less expensive to operative massive clusters at scale.
Presto would only cover the storage/retrival part. Scuba has its own backend for that which is very optimized for the kind of queries the UI needs to support, while Presto is a generic SQL store for analytics.