[jenseng]

There were several factors, but the two big categories were:

1. Familiarity. The original decision to use MySQL was arbitrary, and as the team grew, we just so happened to hire lots of postgres-philes.

2. Death by a million paper cuts. Locking/slowdowns as load increased. Useless EXPLAINs and naive query planning. Truncation (rather than rejection) of VARCHARSs and INTs that exceed length constraints. Having to rewrite queries in weird ways and/or use MySQL-specific syntax to work around performance issues. Lack of partial and expression indexes. No transactional DDL support.

Additionally, the stars aligned. We had a very large customer -- about as big as our other customers combined (up to that point) -- that wanted an on-premise Postgres install, so we added support for it. Eventually the customer opted to move it into our cloud. We didn't want to have to maintain multiple types of database clusters, so we just moved everything to Postgres.