Alibaba has open-sourced their fork of PostgreSQL, wherein they extend the database to support global data consistency, distributed SQL processing, data redundancy, and high availability. PolarDB’s share-nothing distributed architecture enables greater scalability as well as high performance and elasticity. PolarDB slices a table into shards, which are stored in PolarDB nodes, by hashing its primary key. A distributed transaction and transaction coordinator maintains ACID properties across nodes when a query must access shards in many nodes.