[ddorian43]

is there something similar for any opensource rdbms, shard all tables by the same customer_id?

[arielweisberg]

VoltDB makes some similar tradeoffs that allow single sharded SQL to continue to work as expected.

There is actually quite a list of things that are trying to make this work. DBShards, Clustrix, Xeround, and I am sure that isn't all of them.