I tested a MongoDB-to-PostgreSQL sync with a visits collection. At first, I thought the hard part would be the sync itself. It was not. The harder part was making PostgreSQL understand the MongoDB document shape. MongoDB lets one document contain strings, dates, nested objects, arrays, and an _id . PostgreSQL wants fixed columns, clear data types, and a primary key. So before running the sync, I had to decide what the PostgreSQL table should look like. For this test, I used Visua...