Magnus Hagander <magnus@hagander.net> writes:
>>> Specifically, I'm interested if I actually end up making my table any
>>> smaller if I move from 64-bit integer primary key to 32-bit.
>>
>> Depends what else is in the row ... the overall row will get padded to
>> MAXALIGN, but if you were wasting 4 bytes on alignment before, then you
>> win.
> Ah, I see. Followup: Does it make a measurable performance difference
> for things like join or filtering operations, in case the storage size
> ends up being the same?
Hard to say. int8 is pass-by-reference, which is certainly slower than
pass-by-value, but you'd have to measure to see if it makes any
noticeable difference in your queries.
(I imagine someday we'll get around to allowing int8 to be pass-by-value
on 64-bit platforms.)
regards, tom lane