The Record Layer is used by multiple systems at Apple. We demonstrate the power of the Record Layer at scale by de- scribing how CloudKit, Apple’s cloud backend service, uses it to provide strongly-consistent data storage for a large and diverse set of applications [43]. Using the Record Layer’s abstractions, CloudKit offers multi-tenancy at the extreme by maintaining independent record stores for each user of each application. As a result, we use the Record Layer on FoundationDB to host billions of independent databases shar- ing thousands of schemas. In the future, we envision that the Record Layer will be combined with other storage mod- els, such as queues and graphs, leveraging FoundationDB as a general purpose storage engine and remaining transac- tionally consistent across all these models. In summary, this work makes the following contributions:

• An open source layer on top of FoundationDB with se- mantics akin to those of a relational database.

• The record store abstraction and a suite of techniques to manipulate it, enabling billions of logical tenants to operate independent databases in a FoundationDB cluster.

• A highly extensible architecture, clients can customize core features including schema management and indexing.

• A lightweight design that provides rich features on top of

  the underlying key-value store.