Is this correct? I'm fairly sure jsonb supports lazily parsing objects and each object level is actually searched using binary search.
The problem is there's no support for loading just part of a TOASTed field. Even if that existed, we'd still need a way to know what byte position in the TOASTed field a key lived at.
It's possible to add all that, but I think it'd be a serious amount of work.
Since someone else was just wondering about storing more specific types in JSON, it might be more useful/interesting to devise a Postgres-specific way to store variable schema documents. That would give us a lot more flexibility over implementation than the JSON type ever will.
Or think about it this way: there's really no great reason why everyone chose JSON. There's tons of other serialization storage formats for other languages out there, so why not one specialized to Postgres? (And of course we'd want to be able to cast from that to JSON and back...) -- Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX Experts in Analytics, Data Architecture and PostgreSQL Data in Trouble? Get it in Treble! http://BlueTreble.com