Message-ID: <f516d66b-5bed-45af-8127-d09b684dad9e@vondra.me>
Date: Mon, 11 Aug 2025 16:16:05 +0200
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: index prefetching
To: Andres Freund <andres@anarazel.de>
Cc: Peter Geoghegan <pg@bowt.ie>, Nazir Bilal Yavuz <byavuz81@gmail.com>,
 Thomas Munro <thomas.munro@gmail.com>, Robert Haas <robertmhaas@gmail.com>,
 Melanie Plageman <melanieplageman@gmail.com>,
 PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
 Georgios <gkokolatos@protonmail.com>,
 Konstantin Knizhnik <knizhnik@garret.ru>, Dilip Kumar <dilipbalaut@gmail.com>
References: <8ed1d326-5c6e-476e-b3fd-30d3da210546@vondra.me>
 <38b865bd-2ae9-4a94-a788-6e3dc99ccd70@vondra.me>
 <CAH2-WzmER9kc4OtmkDh+h51QV=v6Yc5BGsJikwJHtucf1C1HWw@mail.gmail.com>
 <306fc8c0-c882-4602-86f5-a106b9ace603@vondra.me>
 <CAH2-Wz=0enySZ5g0k0BLY3tHRs=wyG=7yXDYP=Abt=6GM=7XkQ@mail.gmail.com>
 <152ea782-5bd4-4435-b021-0ab2da61e63d@vondra.me>
 <CAH2-WzkX2fwtiNOX4RrBR8=XKta999NM_5+ghTUnwUBkeyfcHQ@mail.gmail.com>
 <7c2f6350-6fca-4e39-b0a8-8ac735f5d58a@vondra.me>
 <CAH2-WzkPh+L2u8_4jG=NgGgzFNqW7ZZhSxGb6mJR=2YdouL1_Q@mail.gmail.com>
 <2e63cadd-2a03-46b1-866e-7ea5d3ffd37f@vondra.me>
 <xhe4l63oxs36sunvqbf3bzlzrondjyhumm7ywt4arkxu622f52@yriy7rejf5g2>
Content-Language: en-US
From: Tomas Vondra <tomas@vondra.me>
In-Reply-To: <xhe4l63oxs36sunvqbf3bzlzrondjyhumm7ywt4arkxu622f52@yriy7rejf5g2>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Archived-At: 
 <https://www.postgresql.org/message-id/f516d66b-5bed-45af-8127-d09b684dad9e%40vondra.me>
Precedence: bulk


On 8/9/25 01:47, Andres Freund wrote:
> Hi,
> 
> On 2025-08-06 16:12:53 +0200, Tomas Vondra wrote:
>> That's quite possible. What concerns me about using tables like pgbench
>> accounts table is reproducibility - initially it's correlated, and then
>> it gets "randomized" by the workload. But maybe the exact pattern
>> depends on the workload - how many clients, how long, how it correlates
>> with vacuum, etc. Reproducing the dataset might be quite tricky.
>>
>> That's why I prefer using "reproducible" data sets. I think the data
>> sets with "fuzz" seem like a pretty good model. I plan to experiment
>> with adding some duplicate values / runs, possibly with two "levels" of
>> randomness (global for all runs, and smaller local perturbations).
>> [...]
>> Yeah, cases like that are interesting. I plan to do some randomized
>> testing, exploring "strange" combinations of parameters, looking for
>> weird behaviors like that.
> 
> I'm just catching up: Isn't it a bit early to focus this much on testing? ISMT
> that the patchsets for both approaches currently have some known architectural
> issues and that addressing them seems likely to change their performance
> characteristics.
> 

Perhaps. For me benchmarks are a way to learn about stuff and better
understand the pros/cons of approaches. It's possible some of the
changes will impact the characteristics, but I doubt it can change the
fundamental differences due to the simple approach being limited to a
single leaf page, etc.

regards


-- 
Tomas Vondra