Re: Changing the default random_page_cost value - Mailing list pgsql-hackers

From Greg Sabino Mullane
Subject Re: Changing the default random_page_cost value
Date
Msg-id CAKAnmmKHzk63bnMZAb5Z5rnYcPjeq+Wfg3pmcnK9rV6cKX2y0A@mail.gmail.com
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In response to Re: Changing the default random_page_cost value  (David Rowley <dgrowleyml@gmail.com>)
Responses Re: Changing the default random_page_cost value
List pgsql-hackers
On Mon, Oct 14, 2024 at 10:20 PM David Rowley <dgrowleyml@gmail.com> wrote:
Yeah, I think any effort to change the default value for this setting would require some analysis to prove that the newly proposed default
is a more suitable setting than the current default. I mean, why 1.2 and not 1.1 or 1.3? Where's the evidence that 1.2 is the best value
for this?

As I said, I was just throwing that 1.2 number out there. It felt right, although perhaps a tad high (which seems right as we keep things very conservative). I agree we should make a best effort to have an accurate, defendable default. We all know (I hope) that 4.0 is wrong for SSDs.
 
I don't think just providing evidence that random read times are closer to sequential read times on SSDs are closer than they are with
HDDs is going to be enough.
... 
It would be nice to have this as a script so that other people could easily run it on their hardware to ensure that random_page_cost we
choose as the new default is representative of the average hardware.

Heh, this is starting to feel like belling the cat (see https://fablesofaesop.com/belling-the-cat.html)

Remember this is still just a default, and we should encourage people to tweak it themselves based on their own workloads. I just want people to start in the right neighborhood. I'll see about working on some more research / generating a script, but help from others is more than welcome.

Cheers,
Greg

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