Realm

Realm Database is an open-source and cross-platform DBMS. Built from the ground in C++, it could support programming languages including Objective-C, Swift, Java and C#.

History

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.

Isolation Levels

Repeatable Read

The MVCC-based Realm Database implements the Repeatable Read isolation level by creating a snapshot at the beginning of the transaction. In this way, dirty-read, non-repeatable and phantom read will be impossible.

Logging

Logical Logging

Realm only maintains the log for the transaction. But it doesn't support the recovery mechanism.

Query Compilation

Not Supported

System Architecture

Embedded

Realm Database is not a distributed database. It's mainly for the mobile device.

Storage Architecture

Hybrid

You could configure during run-time.

Query Interface

Custom API

Realm Database has its own custom APIs.

Views

Virtual Views Materialized Views

Realm database supports reflective views and imperative views. Essentially they are very similar to materialized views and virtual views.

Compression

Bit Packing / Mostly Encoding

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.

Joins

Not Supported

It's not relational database and doesn't support join operations.

Stored Procedures

Not Supported

Data Model

Object-Oriented

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.

Concurrency Control

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.

Storage Model

Decomposition Storage Model (Columnar)

Properties would be kept contiguously linked at the vertical level.

Realm Logo
Website

https://realm.io/products/realm-database

Source Code

https://github.com/realm

Tech Docs

https://realm.io/docs

Developer

Realm

Country of Origin

US

Start Year

2011

Former Name

tight.db

Project Type

Commercial, Open Source

Written in

C++

Supported languages

C#, Java, JavaScript, Objective-C, Swift

Operating Systems

Android, iOS, Windows

Licenses

Apache v2

Wikipedia

https://en.wikipedia.org/wiki/Realm_(database)#Features