Scylla is an open-source distributed NoSQL database. It is compatible with Apache Cassandra, and uses the same protocols (Cassandra Query Language and Thrift) and same file formats (SSTable). It is optimized for workloads that requires low latency and high throughput, in addition to Apache Cassandra's high availability, scalability and fault-tolerance guarantee. Scylla uses a shared-nothing model and shard-per-core architecture, where each thread executes on its own CPU core, memory, and multi-queue network interface controller. Cross-core communication is carried out by explicit message passing, using an event-driven asynchronous programming model, Seastar.


Scylla project is started in 2014 by an Israel startup Cloudius Systems (rebranded as ScyllaDB Inc.), lead by Avi Kivity and Dor Laor. It is a C++ rewritten implementation of Apache Cassandra in Java, and is released as open source in 2015. The current (late 2018) version is 3.0.

Query Interface

Custom API

Scylla uses Cassandra Query Language (CQL) as the Query Interface. Besides, drivers for the following languages are provided: C++, C#, Go, Java, Node.js, PHP, Python, Ruby, and Rust.

Concurrency Control

Multi-version Concurrency Control (MVCC)

Scylla does not support ACID transactions as in RDBMS. However, CQL has a BATCH statement that allows multiple update statements belonging to a given partition key be applied in isolation (note that batches are not a full analogue for SQL transactions). Besides, in UPDATE, INSERT, and DELETE statements, modifications belonging to the same partition key are performed atomically and in isolation. Scylla implements Multi-version Concurrency Control (MVCC) for partition mutation.


Not Supported

Each SELECT statement only applies on one single table.

Isolation Levels

Not Supported

Stored Procedures

Not Supported



Scylla supports non-blocking checkpoints through per-node backup procedures, which include full backup/snapshots and incremental backup. Snapshots are taken by the snapshot operation provided by the nodetool utility, while the incremental backup option can be configured in the configuration file. Automatic unnecessary backup cleaning is not implemented.

Data Model

Column Family

System Architecture


Scylla uses a shared-nothing model. Nodes in the cluster are organized in a decentralized consistent hashing ring and data is partitioned into shards by the key across all nodes. Scylla uses a shard-per-core architecture, where each thread for a shard executes on its own CPU core, memory, and multi-queue network interface controller. Cross-core communication is carried out by explicit message passing. Scylla also uses replicas for fault-tolerance.


Dictionary Encoding

Scylla uses Apache Cassandra chunked compression on SSTable files. Three dictionary-based compression algorithms are provided: LZ4 (default), Snappy, and DEFLATE. Data needs to be decompressed before being processed during query execution.

Scylla Logo

Source Code

Tech Docs


ScyllaDB Inc.

Country of Origin


Start Year


Project Type

Commercial, Open Source

Written in


Supported languages

C#, C++, Go, Java, JavaScript, PHP, Python, Ruby, Rust

Derived From


Compatible With


Operating Systems