Short version: In our case, the move from flat data to nested data was the killer...We came up with a sweet way of storing the nested data and abstracting away

Short version: In our case, the move from flat data to nested data was the killer...We came up with a sweet way of storing the nested data and abstracting away most of complexities of dealing all kinds of data...However, the load on our database was far more than we envisioned...MySQL.