Erleans, https://github.com/erleans/erleans, also supports Postgres for state storage for stateful grains.

I use binary term for this in the 2 provided state backends:

But the providers themselves decide whether to use a binary term or something else like json (or protobuf, etc). There certainly could be advantages to json, like if you for some reason wanted to query the state of grains (your processes) in the postgres table, but I think term_to_binary suits most needs.

The only issue with term_to_binary is technically you could run into problems when moving between versions of OTP. And definitely would if records were used (but since you are in Elixir you don’t have that worry). Which is why Orleans suggests JSON https://dotnet.github.io/orleans/Documentation/grains/grain_persistence/index.html#recommendations

Having a Postgres table with just id and metadata field (jsonb Postgres type for maps) worked quite fine for me in the past.