Realm Database comes from the YCombinator LLC. which was founded by Alexander Stigsen and Bjarne Christiansen in 2011. They started the project called TightDB in the end of 2010 and renamed it to Realm in September, 2014. Realm was officially announced and open-sourced to the developers from over the world in 2016. Later in January 2017 its first stable version was released.
Multi-version Concurrency Control (MVCC)
In order to support concurrent read/write operations under the constraint of data consistency, the Realm Database implements Multi-version Concurrency Control based on copy-on-write mechanism. Every time a new transaction begins, the database would create a snapshot of the database and all the following read/write operations will be done on the snapshot without any modification on the existing data. Only when the transaction commits or aborts will the database verify everything and atomically persist the changes into the disk safely based on two-phase commit protocol. Under this architecture, threads that concurrently read/write the data will not be affected by each other and the data in database will be intact even if the write operations are interrupted because of the software failure.
Realm Database is an object-oriented database built from scratch instead of using an existing relational database. Application development related to objects will always encounter the mismatch between the object layer and database layer and one of the popular solution to this problem is to utilize the ORM while it is not straightforward and smooth in development experience. In this way, Realm Database provides the developers with an object interface based on object-oriented data model.
Decomposition Storage Model (Columnar)
Properties would be kept contiguously linked at the vertical level.
Virtual Views Materialized Views
Realm database supports reflective views and imperative views. Essentially they are very similar to materialized views and virtual views.
The Realm Database supports the features that optimize the memory usages for some data structures. For example, the database will convert a giant list of strings into enums, which is similar to the tagger pointers in Objective-C, in order for fast lookup. Moreover, the database utilizes integer packing to store the integer with optimized space so that it is not necessary to specify the integer type when declaration.
https://realm.io/products/realm-database
Realm
2011
tight.db
C#, Java, JavaScript, Objective-C, Swift