Re: [HACKERS] Some notes on optimizer cost estimates

At 01:13 PM 1/24/00 -0500, Tom Lane wrote:

>In practice this would be happening at initdb time, not configure time,
>since it'd be a lot easier to do it in C code than in a shell script.
>But that's a detail. I'm still not clear on how you can wave away the
>issue of kernel disk caching --- if you don't use a test file that's
>larger than the disk cache, ISTM you risk getting a number that's
>entirely devoid of any physical I/O at all.

And even the $100 6.4 GB Ultra DMA drive I bought last week has
2MB of cache. hdparm shows me getting 19 mB/second transfers
even though it adjusts for the file system cache. It's only a
5400 RPM disk and I'm certain the on-disk cache is impacting
this number.

- Don Baccus, Portland OR <dhogaza(at)pacifier(dot)com>
Nature photos, on-line guides, Pacific Northwest
Rare Bird Alert Service and other goodies at
http://donb.photo.net.