History[06][07][08]

Started with the project Emit Cloud, which is a file synchronization application like Dropbox, the developers at Biokoda found problems in achieving no single point of failure and horizontal scalability. To solve the problem, developers at Biokoda extended SQLite's WAL format to implement Raft. In the later versions, LMDB is used as the storage engine for ActorDB. ActorDB was first launched in 2014. The latest official stable release is 0.10.27 (Jan 2019).

Checkpoints[09]

ActorDB does not require checkpoints from WAL to the main database file.

Concurrency Control[10][11]

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

Data Model[03][02]

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

Foreign Keys[12][13]

Foreign keys are enabled by default in ActorDB.

Indexes[14]

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

Isolation Levels[15]

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

Joins[14]

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

Logging[09]

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

Query Execution[14]

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

Query Interface[16][02]

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 and recommended to use the thrift interface, which supports more popular languages.

Storage Architecture[15][17]

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

Storage Model[17]

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.

Storage Organization

System Architecture[18]

ActorDB has clusters that have 1, 3, or 5 nodes, each of which contains about 4 shards.

Views[16]

ActorDB currently doesn't support MapReduce.