"Jim C. Nasby" <jim@nasby.net> writes:
> Dumb question... wouldn't getting down to 20 bytes buy us something?
Only on 32-bit machines, which are getting less interesting as database
servers every day. (Just last night I was reading somebody opining that
the transition to 64-bit hardware would be effectively complete by 2008
... and he was talking about desktop PCs, not serious iron.)
BTW, the apparently useless byte after the 27- or 23-byte header
actually has some good use: in a table of up to 8 columns, you can
fit a null bitmap there "for free". In a scheme that took us down
to 20 rather than 19 bytes, even a narrow table would pay the full
maxalign price for having a null.
I'm in favor of combining cmin/cmax/xvac to get us down to 23 bytes,
but I think anything beyond that is going to face a serious problem
of greatly increased cost for diminishing returns.
regards, tom lane
