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Re: Padding on 64-bit

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Magnus Hagander <magnus(at)hagander(dot)net>
Cc: PGSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Padding on 64-bit
Date: 2007-05-29 20:01:45
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Lists: pgsql-hackers
Magnus Hagander <magnus(at)hagander(dot)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

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