@sag47 Because the support for postgres is conditional. For example here: https://github.com/gitlabhq/gitlabhq/blob/master/app/models/user.rb#L202 after https://github.com/gitlabhq/gitlabhq/commit/12420a2256168a122b3a1f5a2c974df52fe802ec postgress falls to his death. If the tests were run with postgres - it would have been long known. Here https://github.com/gitlabhq/gitlabhq/commit/be817c53c6fcf946bc149b2e603e3809e79d9d36 @randx remove postgres from test run. 

Gitlab can work with postgres after some little fixes. Mysql is mainstream.