They are possible but they are not possible to make per formant compared to the alternative.

Google falls under the "absurd amount of money" camp.

> Protocol Buffers have performance implications for query processing. First, we always have to fetch entire Protocol Buffer columns from Spanner, even when we are only interested in a small subset of fields.

There are a number of performance costs documented in the paper. Simply because you can solve it via money doesn't mean it works for all situations.