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From: Tomas Vondra <[email protected]>
To: Andres Freund <[email protected]>
Cc: Peter Geoghegan <[email protected]>
Cc: Nazir Bilal Yavuz <[email protected]>
Cc: Thomas Munro <[email protected]>
Cc: Robert Haas <[email protected]>
Cc: Melanie Plageman <[email protected]>
Cc: PostgreSQL Hackers <[email protected]>
Cc: Georgios <[email protected]>
Cc: Konstantin Knizhnik <[email protected]>
Cc: Dilip Kumar <[email protected]>
Subject: Re: index prefetching
Date: Mon, 11 Aug 2025 16:16:05 +0200
Message-ID: <[email protected]> (raw)
In-Reply-To: <xhe4l63oxs36sunvqbf3bzlzrondjyhumm7ywt4arkxu622f52@yriy7rejf5g2>
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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

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