Re: Optimization of the alignment padding

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Alvaro Herrera <alvherre(at)commandprompt(dot)com> writes:
> > There was a discussion during the 8.1 devel cycle about shortening the
> > HeapTupleHeader struct.
>
> It would, in fact, largely eliminate the point of this patch, since the
> standard header size would go back to being a multiple of 8.

Yes, I know the discussion, but I think it and this patch don't conflict.
These spaces don't disappear completely even if the shortening improvement
has done, ex. for tuples that have 2 bytes or more null-bitmaps.

> the internal padding within the tuple depends on what
> alignment the start was at

Tuple headers must be located at a MAXALIGN boundary,
so internal padding does not change as long as a relative position
between the header and the first field is fixed.

but...

> It will probably actually break some
> places, because I think we sometimes attach a data area to a separately
> created header.

Thanks, I didn't consider it.
I'll check the cases and whether they can be resolved.

---
ITAGAKI Takahiro
NTT Cyber Space Laboratories