Re: HOT for PostgreSQL 8.3

On 2/13/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> > Hannu Krosing wrote:
> >> Are we actually doing that ? I.E are null bitmaps really allocated in 1
> >> byte steps nowadays ?
>
> > Yes.
>
> Not really; we still have to MAXALIGN at the end of the bitmap. The
> point is that you can get 8 bits in there before paying the first
> additional MAXALIGN increment.
>
> It's all moot anyway since 8 bits isn't enough for a pointer ...
>
>
We could live with 8 bits actually. We can store only the least
significant 8 bits of the pointer. It would point to a set of tuples and
we may need to search within that set to find the required tuple.
This would still be better than scanning the entire page.

But I agree that utilizing those 8 bits would result in a penalty
for tables with few columns.

Thanks,
Pavan

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