Compression

Naïve (Page-Level)

Pages are compressed in ActorDB using LZ4, which is a general-purpose algorithm.

Isolation Levels

Serializable

Every actor is an SQLite database, where all transactions are serializable.

Checkpoints

Not Supported

Using LMDB as the storage engine, ActorDB stores pages in an append-only style. It replaces SQLite's WAL implementation, and checkpoints are replaced with cleanups that free up space.

Storage Organization

Copy-on-Write / Shadow Paging

Query Execution

Tuple-at-a-Time Model

ActorDB uses SQLite as its query engine, which uses Volcano-style query processing.

System Architecture

Shared-Nothing

ActorDB has clusters that have 1, 3, or 5 nodes, each of which contains about 4 shards. The nodes act as independent actors who share no common memory or storage.

Logging

Physical Logging

ActorDB uses Raft protocol to replicate actors. The protocol is extended on SQLite WAL module and requires a write log to operate.

Storage Architecture

In-Memory

ActorDB uses LMDB as its storage engine. Each actor is stored within an LMDB file. LMDB uses mmap to achieve in memory storage.

Views

Not Supported

Concurrency Control

Multi-version Concurrency Control (MVCC) Not Supported

Although ActorDB is concurrent on the database level, it is not on each actor. The storage engine LMDB employs MVCC.

Indexes

B+Tree

ActorDB uses SQLite as the query engine, which uses B-Tree for its default indexing data structure.

Foreign Keys

Supported

Foreign keys are enabled by default in ActorDB.

Joins

Nested Loop Join

Each actor runs SQLite as the query engine, which uses Nested Loop Join.

Storage Model

Custom

As the storage engine being used, LMDB uses a memory-map to store the database with copy-on-write semantics, hence no specific storage model.

Query Interface

Custom API SQL

ActorDB doesn't need any special drivers, as developers can use MySQL driver of the language of choice. ActorDB is connectable over the MySQL protocol. It is also connectable to the thrift interface, which supports more popular languages.

Data Model

Relational

ActorDB is a distributed relational database. But it also has the scalability of a Key-Value(KV) store by introducing a KV data type, which is a SQL table that is partitioned across all servers.