Re: [RFC] Lock-free XLog Reservation from WAL

On Wed, 22 Jan 2025 at 17:02, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru> wrote:
> I believe, I know why it happens: I was in hurry making v2 by
> cherry-picking internal version. I reverted some changes in
> CalcCuckooPositions manually and forgot to add modulo
> PREV_LINKS_HASH_CAPA.
>
> Here's the fix:
>
> pos->pos[0] = hash % PREV_LINKS_HASH_CAPA;
> - pos->pos[1] = pos->pos[0] + 1;
> + pos->pos[1] = (pos->pos[0] + 1) % PREV_LINKS_HASH_CAPA;
> pos->pos[2] = (hash >> 16) % PREV_LINKS_HASH_CAPA;
> - pos->pos[3] = pos->pos[2] + 2;
> + pos->pos[3] = (pos->pos[2] + 2) % PREV_LINKS_HASH_CAPA;
>
> Any way, here's v3:
> - excess file "v0-0001-Increase..." removed. I believe it was source
> of white-space apply warnings.
> - this mistake fixed
> - more clear slots strategies + "8 positions in two cache-lines" strategy.
>
> You may play with switching PREV_LINKS_HASH_STRATEGY to 2 or 3 and see
> if it affects measurably.

Thanks for your quick fixing. I will retest it tomorrow.

--
Regrads,
Japin Li