| From: | Heikki Linnakangas <hlinnaka(at)iki(dot)fi> |
|---|---|
| To: | Dhruv Aron <dhruv(dot)aron(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com> |
| Cc: | pgsql-hackers(at)postgresql(dot)org, haoyu(dot)huang(dot)68(at)gmail(dot)com |
| Subject: | Re: Restructured Shared Buffer Hash Table |
| Date: | 2026-08-05 16:02:27 |
| Message-ID: | 6a184a00-0799-4d47-88ac-27645db2b0ad@iki.fi |
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| Lists: | pgsql-hackers |
On 10/07/2026 21:53, Dhruv Aron wrote:
> On Tue, 7 Jul 2026 at 20:14, Heikki Linnakangas <hlinnaka(at)iki(dot)fi
> <mailto:hlinnaka(at)iki(dot)fi>> wrote:
> > Or maybe it's not a problem, in which case some kind of a
> > worst case scenario benchmark to show that would be nice. Maybe test how
> > it behaves when you have a lot of hash collisions, I think that'd make
> > BufTableDelete() more expensive.
>
> My additional benchmarking would suggest that, on average (one entry per
> bucket), the spinlock would be held for an extra ~50ns compared to
> releasing the header lock earlier for the current dynahash implementation:
It's not clear to me what the impact of that is in practice. Is that a
problem or not? Can you come up with an adversary test case where those
conflicts cause a lot of spinning?
Can you share the benchmark you used, please?
- Heikki
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