| From: | Peter Geoghegan <pg(at)bowt(dot)ie> |
|---|---|
| To: | Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | Tomas Vondra <tomas(at)vondra(dot)me>, Thomas Munro <thomas(dot)munro(at)gmail(dot)com>, Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Melanie Plageman <melanieplageman(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Georgios <gkokolatos(at)protonmail(dot)com>, Konstantin Knizhnik <knizhnik(at)garret(dot)ru>, Dilip Kumar <dilipbalaut(at)gmail(dot)com> |
| Subject: | Re: index prefetching |
| Date: | 2025-11-24 21:38:15 |
| Message-ID: | CAH2-Wzm6yf7rLAzmpnEnvc_0E5y-2p_pTQ++TNxdQgo=VnZLQQ@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Nov 24, 2025 at 3:48 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> Huh. I wouldn't have expected -march=native to make a huge difference...
Me neither. On the other hand I find that this area is quite sensitive
to icache misses and branch misprediction penalties. This is partly
due to my holding the patch to a very high standard, in terms of
avoiding regressions (at least for simple point lookup queries and
nestloop join queries).
> I don't think the precise gains here, particularly basedon on quick
> prototypes, make that much of a difference. There's so much more optimization
> potential other than the amortization of locking costs...
I agree that this precise issue isn't necessarily all that important.
My current focus is on completely separating the I/O prefetching parts
of the patch from the core AM interface changes, while avoiding
regressions shown by various microbenchmarks. My experiments with
-march=native were mostly about that -- not about the heap buffer
locking thing specifically. That was just something I noticed in
passing, and found curious.
--
Peter Geoghegan
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