Hardware Acceleration

Custom

No Acceleration

Storage Organization

Copy-on-Write / Shadow Paging

Concurrency Control

Multi-version Concurrency Control (MVCC)

In Realm, each connected thread will see a snapshot of the data at a particular point in time. Moreover, it utilizes the copy-on-write mechanism and allows only one client to modify data at a certain point.

Isolation Levels

Read Uncommitted

No objects shared between threads, which means it's literally single-thread.

Data Model

Object-Oriented

Foreign Keys

Supported

Not Supported

Storage Architecture

Hybrid

You could configure during run-time.

System Architecture

Embedded

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

Stored Procedures

Not Supported

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.

Query Compilation

Not Supported

Logging

Logical Logging

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

Joins

Not Supported

It's not relational database

Views

Virtual Views Materialized Views

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

Indexes

B+Tree

Realm is based on B- Tree Structure

Storage Model

Decomposition Storage Model (Columnar)

Properties would be kept contiguously linked at the vertical level.

Query Interface

Custom API

Realm Database has its own custom APIs.