Re: Database file compatability

"Qingqing Zhou" <zhouqq(at)cs(dot)toronto(dot)edu> writes:
> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote in message
> There is a possible sequence like this:

> ALIGNOF_LONG 4
> ALIGNOF_DOUBLE 8
> MAXIMUM_ALIGNOF 8

> vs.

> ALIGNOF_LONG 8
> ALIGNOF_DOUBLE 8
> MAXIMUM_ALIGNOF 8

> So we should at least check ALIGNOF_LONG as well.

No, we don't need to, because we do not really care about ALIGNOF_LONG
per se. We don't use "long" as an on-disk datatype, precisely because
we don't know what size it is. We use int32 and int64. The former has
align 4 on all machines AFAIK, and the latter has MAXIMUM_ALIGNOF.

> There are some machines with sizeof(int) equals to 64, if my memory saves,
> which might imply that ALIGNOF_INT equals to 8.

If there were such a machine, Postgres wouldn't run on it anyway, and
a lot of other software too. There'd be no way to have both int16 and
int32 types ("short" could cover only one of them).

regards, tom lane