WebScaleSQL was an open-source relational database management system (RDBMS) created as a software branch of the production-ready community releases of MySQL.

[3][6][7] WebScaleSQL was announced on March 27, 2014 as a joint effort of Facebook, Google, LinkedIn and Twitter (with Alibaba Group joining in January 2015[8]), aiming to provide a centralized development structure for extending MySQL with new features specific to its large-scale deployments, such as building large replicated databases running on server farms.

As a result, WebScaleSQL attempted to open a path toward deduplicating the efforts each founding company had been putting into maintaining its own branch of MySQL, and toward bringing together more developers.

[1][4][9] WebScaleSQL was created as a branch of the MySQL's latest production-ready community release, which was version 5.6 as of March 2013[update].

[1][3][4] The initial changes and feature additions that WebScaleSQL introduced to the MySQL 5.6 codebase came from the engineers employed by the four founding companies; however, the project was open to peer-reviewed community contributions.