Magnus Hagander <[EMAIL PROTECTED]> 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

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TIP 9: In versions below 8.0, the planner will ignore your desire to
       choose an index scan if your joining column's datatypes do not

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