After a fair amount of community feedback and research the core team is preparing to change from MySQL in the recommended default install to PostgreSQL before the 1.0.0 release of Mattermost.
While MySQL is currently more popular (and currently its interface is more compatible with cloud services), in speaking with the open source community that’s been growing around Mattermost, the growth in quality, improvements and adoption from PostgreSQL is unparalleled.
MariaDB was also considered, but the majority of community support has been for PostgreSQL, so that’s where the project is going next.
Many thanks to everyone who voted and weighed in. The earliest days of a project are the best time to influence its direction, and you folks have.