Postgres CAN do exactly this, in fact, this is the sort of thing it excels at, the transactions in postgres can do this, and so much more. I think what you're

Postgres CAN do exactly this, in fact, this is the sort of thing it excels at, the transactions in postgres can do this, and so much more. I think what you're talking about is appending with a single statement, which Postgres can also do. You can deserialize JSON inside a postgres query, alter parts of it, serialize it again, then store it in a single atomic transaction using an UPDATE.