Braintree Payments uses PostgreSQL as its primary datastore. We rely heavily on the data safety and consistency guarantees a traditional relational database offers us, but these guarantees come with certain operational difficulties. To make things even more interesting, we allow zero scheduled functional downtime for our main payments processing services.
Several years ago we published a blog post detailing some of the things we had learned about how to safely run DDL (data definition language) operations without interrupting our production API traffic.
Since that time PostgreSQL has gone through quite a few major upgrade cycles — several of which have added improved support for concurrent DDL. We’ve also further refined our processes. Given how much has changed, we figured it was time for a blog post redux.