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From: Tom Lane <[email protected]>
To: David Rowley <[email protected]>
Cc: Greg Sabino Mullane <[email protected]>
Cc: Dagfinn Ilmari Mannsåker <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Bruce Momjian <[email protected]>
Subject: Re: Changing the default random_page_cost value
Date: Mon, 14 Oct 2024 23:03:59 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAKAnmmK_nSPYr53LobUwQD59a-8U9GEC3XGJ43oaTYJq5nAOkw@mail.gmail.com>
	<[email protected]>
	<CAKAnmmKxOq8i4JCfc6AzThuetLPenGaOQu25m0EeOhanaQdhLw@mail.gmail.com>
	<[email protected]>
	<CAApHDvrRzq_XO=4PPamY6gr8OLquVXYBMen8+=op0UjmF6vk0g@mail.gmail.com>
	<[email protected]>

I wrote:
> I recall that when we settled on 4.0 as a good number for
> spinning-rust drives, it came out of some experimentation that
> I'd done that involved multiple-day-long tests.  I don't recall any
> more details than that sadly, but perhaps trawling the mailing list
> archives would yield useful info.  It looks like the 4.0 value came
> in with b1577a7c7 of 2000-02-15, so late 1999/early 2000 would be the
> time frame to look in.

I tried asking https://www.postgresql.org/search/ about
random_page_cost, and got nothing except search engine timeouts :-(.
However, some digging in my own local archives yielded

https://www.postgresql.org/message-id/flat/25387.948414692%40sss.pgh.pa.us

https://www.postgresql.org/message-id/flat/14601.949786166%40sss.pgh.pa.us

That confirms my recollection of multiple-day test runs, but doesn't
offer much more useful detail than that :-(.  What I think I did
though was to create some large tables (much bigger than the RAM on
the machine I had) and actually measure the runtime of seq scans
versus full-table index scans, repeating plenty 'o times to try to
average out the noise.  There was some talk in those threads of
reducing that to a publishable script, but it was never followed up
on.

			regards, tom lane

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