Distributed SQL

A distributed SQL database is a single relational database which replicates data across multiple servers. Distributed SQL databases are strongly consistent and most support consistency across racks, data centers, and wide area networks including cloud availability zones and cloud geographic zones. Distributed SQL databases typically use the Paxos or Raft algorithms to achieve consensus across multiple nodes.

Sometimes distributed SQL databases are referred to as NewSQL but NewSQL is a more inclusive term that includes databases that are not distributed databases.

 – meaning data represented as tables with rows and columns similar to any other RDBMS

automatically sharded data storage

underlying key–value storage

native SQL implementation

Following the CAP Theorem, distributed SQL databases are "CP" or consistent and partition-tolerant. Algorithmically they sacrifice availability in that a failure of a primary node can make the database unavailable for writes.

All distributed SQL implementations require some kind of temporal synchronization to guarantee consistency. With the exception of Spanner, most do not use custom hardware to provide atomic clocks. Spanner is able to synchronize writes with temporal guarantees. Implementations without custom hardware require servers to compare clock offsets and potentially retry reads.

Vendor	API	License model
Amazon Aurora	PostgreSQL & MySQL	Proprietary
CockroachDB	PostgreSQL-like	Proprietary
Google Spanner	Proprietary SQL-like	Proprietary
MySQL Cluster	MySQL	Open Source (GPLv2)
NuoDB	Proprietary SQL	Proprietary
YugabyteDB	PostgreSQL & Cassandra CQL-like	Open Source (Apache 2.0)
TiDB	MySQL-like	Open Source (Apache 2.0)
MariaDB XPand	MariaDB	Proprietary
Teradata	Proprietary SQL-like	Proprietary
YDB	Proprietary SQL-like, PostgreSQL-like	Open Source (Apache 2.0)

CockroachDB, YugabyteDB and others have at times referred to themselves as NewSQL databases. Some of the NewSQL databases have fundamentally different architectures, but were cited as examples of NewSQL by Matthew Aslett who coined the term. In essence, distributed SQL databases are built from the ground-up and NewSQL databases include replication and sharding technologies added to existing client-server relational databases like PostgreSQL. Some experts define DistributedSQL databases as a more specific subset of NewSQL databases.

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