Re: Changing the default random_page_cost value

Bruce Momjian <bruce@momjian.us> writes:
> On Thu, Oct 24, 2024 at 08:01:11PM -0400, Greg Sabino Mullane wrote:
>> Okay, but we have no documented logic on why 4.0 was chosen either. :)

> Uh, we do, and it is in the docs:

>         Random access to mechanical disk storage is normally much more expensive
>         than four times sequential access.  However, a lower default is used
>         (4.0) because the majority of random accesses to disk, such as indexed
>         reads, are assumed to be in cache.  The default value can be thought of
>         as modeling random access as 40 times slower than sequential, while
>         expecting 90% of random reads to be cached.

Meh.  Reality is that that is somebody's long-after-the-fact apologia
for a number that was obtained by experimentation.

			regards, tom lane