[dunham]

Datomic basically does the same thing your database does - caching the working set in memory and running the queries. The difference is that with datomic the db is running in your java process rather than on another server. This should get you better scalability (for reads) and make complex queries faster. (Writes still go through a designated server.)

The data is modeled as a collection of (entity,property,values,txn) tuples (with schema on property). They are stored in a log and a few ordered sets (indexes) that are structured somewhat like 2-layer btrees with large pages. These pages and the tail of the log are loaded as needed while running queries. The nature of the data model also gets you point in time queries and queries across time (e.g. all previous values of a property).