> In fact, I don't think there's any low-level data format changes yet
> between 8.3 and 8.4, so this would be a comparatively easy release to
> implement upgrade-in-place. There's just the catalog changes, but AFAICS
> nothing that would require scanning through relations.
After a quick scan of the catversion.h changelog (which hopefully covers
any such changes): we changed sequences incompatibly, we changed hash
indexes incompatibly (even without the pending patch that would change
their contents beyond recognition), and Teodor did some stuff to GIN
indexes that might or might not represent an on-disk format change,
you'd have to ask him. We also whacked around the sort order of
bpchar_pattern_ops btree indexes.
I didn't see anything that looked like an immediate change in user table
contents, unless they used the "name" type; but what of relation forks?
regards, tom lane