[dcosson]

Interesting that sharding by customer for a sass business is the example of the best use of sharding. That can also go very wrong - what if you get a huge customer that's as big as everyone else combined? You're effectively maxed out at 2 shards.

Definitely depends on the workload, but often the "micro service" approach (whether or not it's a true micro service in its own runtime) of sharding just one type of data/small set of related tables that you can shard by a primary key or user id or something seems like the only reasonable option for sharding. If your data is becoming unwieldy there's often a bottleneck data set that's bigger than everything else so you don't necessarily have to share everything all at once.