Re: GIN improvements part 1: additional information

On Fri, Oct 4, 2013 at 12:28 PM, Heikki Linnakangas <hlinnakangas(at)vmware(dot)com
> wrote:

> Aside from the pg_upgrade discussion, here's an updated version of the
> patch, rebased over master. It also contains some other misc refactoring
> I've done while reading through the patch. I haven't tested this much, I
> may well have also broken something, but I wanted to post an update before
> the weekend.
>
> Thinking about the page format, I think we should start using the
> pd_lower/upper pointers in the data page format. For a non-leaf page,
> pd_upper would always point to the beginning of the special area, and
> pd_lower would indicate the end of PostingItems. For a leaf page, pd_lower
> would indicate the end of the compressed posting list, and pd_upper would
> point to the "leaf-index" at the end of the page. That matches the standard
> page layout in the sense that the space between pd_lower and pd_upper is
> free, although the data stored in the non-free areas would be quite
> different. That would allow us to mark full-page images with buffer_std,
> allowing the "gap" to be left out. I think that would be a more natural way
> to keep track of the used/unused space on the page, anyway, compared to the
> current maxoff/endoffset field in the special area.
>
> In the attached patch, I in fact already did that for data leaf pages, but
> didn't change the format of non-leaf pages yet. If we want to support
> pg_upgrade, we might want to refrain from changing the non-leaf format.

In GinDataLeafPageGetPostingList* you use sizeof(ItemPointerData) without
MAXALIGN. Is it an error or you especially use 2 extra bytes on leaf page?

------
With best regards,
Alexander Korotkov.