On Fri, Jan 06, 2006 at 04:20:15PM -0000, Greg Sabino Mullane wrote:
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> > Every time this idea is brought up, people seem to think that the idea
> > is to produce some ideal configuration out-of-the-box, which of course
> > is exceptionally difficult. But *anything* would be far superior to what
> > we have now. Clearly there's no replacement for actually going in and
> > tuning things by hand, and anyone with any kind of database knowledge
> > will know that.
>
> On a sort of related note, I recall lobbying for dropping the
> random_page_cost down from the current default of 4, but getting
> shot down because random_page_cost was part of a bigger picture and
> adjusting that alone was the Wrong Way To Do It. Nothing ever came of
> it however, so I invariably end up adjusting random_page_cost on every
> install I do.
The issue is that testing of the cost of random vs sequential access on
modern hard drives still shows that 4 is the correct value. The reason
people end up decreasing it is because of shortcommings in the various
estimator functions; decreasing random_page_cost brings the estimates
closer to reality, but it's the wrong way to go about it.
So it's another case of year after year of shipping a bad default
configuration because "some day we'll get around to fixing the problem
the right way".
--
Jim C. Nasby, Sr. Engineering Consultant jnasby@pervasive.com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461