"Dave Page" <dpage@vale-housing.co.uk> writes:
> It's rumoured that Hiroshi Inoue once said:
>> Does looking up by the catalog keys take no cost ?
> Obviously there is cost, but doing a lookup only on demand, has got to be
> cheaper in the long run than including the entire column definition in the
> message whether it's wanted or not?
More to the point, the cost is paid by applications that want the
functionality, and not by those that don't.
It'd probably be reasonable for client libraries to maintain a cache
of column info, so that they only have to query the backend about a
particular column ID once per connection. (This is one reason why
I want attrelid/attnum to be the info given on the wire: it's stable
enough to be used over a whole session to index such a cache. Names
could not safely be used that way.)
regards, tom lane