Re: WIP: extensible enums

Robert Haas <robertmhaas@gmail.com> writes:
> I suppose you could fix this by always updating every row, and storing
> in each row the total count of elements (or a random number).  Then
> it'd be obvious if you'd read an inconsistent view of the world.

Well, the easy way to read a consistent view of the world is to load the
cache using an MVCC snapshot instead of SnapshotNow.  The current code
structure isn't amenable to that because it's relying on a syscache to
fetch the data for it, but that seems pretty inefficient anyway.  I'm
thinking of changing it around so that the enum cache gets loaded with
a regular systable_beginscan() scan, and then we could load with an
MVCC snapshot.

I'm kind of inclined to go to the float-based representation anyway,
though, just because not having to update other rows to do an insert
seems like a good thing.  But we could combine that with an MVCC
snapshot on the read side, which would make renumbering safe, which
would mean that we could auto-renumber when we ran out of code space
and not otherwise.  Is that getting too complicated?
        regards, tom lane