Martijn van Oosterhout <kleptog(at)svana(dot)org> writes:
> Do they actually save spaces (consider alignment issues and such)?
WITHOUT OIDS doesn't currently save any space --- the tuple header
layout is the same either way. It should save a few microseconds
per row inserted (since you don't have to generate an OID) but
that's about it.
The main reason for inventing the feature was to postpone OID-counter
wraparound in large installations. Wraparound isn't fatal, but can
be annoying --- for example, pg_dump may get confused about the best
order to dump tables in.
regards, tom lane