> If your Postgres JSON schema modified for new application requirements, the table is locked until existing data is copied into the new schema, requiring applications to be quiesced during schema migration.

Are you saying that if you INSERT a row with a new JSONB property that wasn't previously included in any of the rows of that table, then the entire table gets locked while all rows are copied. And if so, do you have a source for that? I can't find anything through google.