Re: Confine vacuum skip logic to lazy_scan_skip

On Sat, Jan 18, 2025 at 11:51 AM Tomas Vondra <tomas(at)vondra(dot)me> wrote:
>
> Sure. I repeated the benchmark with v13, and it seems the behavior did
> change. I no longer see the "big" regression when most of the pages get
> updated (and need vacuuming).
>
> I can't be 100% sure this is due to changes in the patch, because I did
> some significant upgrades to the machine since that time - it has Ryzen
> 9900x instead of the ancient i5-2500k, new mobo/RAM/... It's pretty
> much a new machine, I only kept the "old" SATA SSD RAID storage so that
> I can do some tests with non-NVMe.
>
> So there's a (small) chance the previous runs were hitting a bottleneck
> that does not exist on the new hardware.
>
> Anyway, just to make this information more complete, the machine now has
> this configuration:
>
> * Ryzen 9 9900x (12/24C), 64GB RAM
> * storage:
> - data: Samsung SSD 990 PRO 4TB (NVMe)
> - raid-nvme: RAID0 4x Samsung SSD 990 PRO 1TB (NVMe)
> - raid-sata: RAID0 6x Intel DC3700 100GB (SATA)
>
> Attached is the script, raw results (CSV) and two PDFs summarizing the
> results as a pivot table for different test parameters. Compared to the
> earlier run I tweaked the script to also vary io_combine_limit (ioc), as
> I wanted to see how it interacts with effective_io_concurrency (eic).
>
> Looking at the new results, I don't see any regressions, except for two
> cases - data (single NVMe) and raid-nvme (4x NVMe). There's a small area
> of regression for eic=32 and perc=0.0005, but only with WAL-logging.
>
> I'm not sure this is worth worrying about too much. It's a heuristics
> and for every heuristics there's some combination parameters where it
> doesn't quite do the optimal thing. The area where the patch brings
> massive improvements (or does not regress) are much more significant.
>
> I personally am happy with this behavior, seems to be performing fine.

Yes, looking at these results, I also feel good about it. I've updated
the commit metadata in attached v14, but I could use a round of review
before pushing it.

- Melanie