Re: [HACKERS] Solution for LIMIT cost estimation

At 06:43 PM 2/13/00 -0500, Tom Lane wrote:

>Ah, you haven't seen the (as-yet-uncommitted) optimizer changes I'm
>working on ;-)

Very good!

>What I still lack is a believable approximation curve for cache hit
>ratio vs. table-size-divided-by-cache-size. Anybody seen any papers
>about that? I made up a plausible-shaped function but it'd be nice to
>have something with some actual theory or measurement behind it...
>
>(Of course the cache size is only a magic number in the absence of any
>hard info about what the kernel is doing --- but at least it will
>optimize big tables differently than small ones now.)

If you've got the memory and allocate sufficient space to shared
buffers and still have plenty of kernel cache space left over, the
optimizer can hardly be over optimistic - things will fly! :)

- 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.