| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Peter Geoghegan <pg(at)bowt(dot)ie>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Lowering the ever-growing heap->pd_lower |
| Date: | 2022-04-08 21:18:15 |
| Message-ID: | 20220408211815.jac65f5qlmu43sjj@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2022-04-08 15:04:37 -0400, Robert Haas wrote:
> I meant wasting space in the page. I think that's a real concern.
> Imagine you allowed 1000 line pointers per page. Each one consumes 2
> bytes.
It's 4 bytes per line pointer, right?
struct ItemIdData {
unsigned int lp_off:15; /* 0: 0 4 */
unsigned int lp_flags:2; /* 0:15 4 */
unsigned int lp_len:15; /* 0:17 4 */
/* size: 4, cachelines: 1, members: 3 */
/* last cacheline: 4 bytes */
};
Or am I confusing myself somehow?
I do wish the length of the tuple weren't in ItemIdData, but part of the
tuple, so we'd not waste this space for dead items (I think it'd also simplify
more code than it'd complicate). But ...
- Andres
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