On 06/11/2020 19:57, Justin Pryzby wrote:
On Fri, Nov 06, 2020 at 01:51:26PM +0000, Anastasia Lubennikova wrote:
The first patch is simply a refactoring and don't see any possible objections
against it.
The second patch also looks fine to me. The logic is understandable and the
code is neat.
+1
It wouldn't hurt to add a comment for this computation, though.
+ pages_fetched = pages_fetchedMAX +
indexCorrelation*indexCorrelation*(pages_fetchedMIN - pages_fetchedMAX);
You're right. It's like this:
// interpolate between c==0: pages_fetched=max and c==1: pages_fetched=min
pages_fetched = min + (max-min)*(1-c**2)
pages_fetched = min + max*(1-c**2) - min*(1-c**2)
pages_fetched = max*(1-c**2) + min - min*(1-c**2)
pages_fetched = max*(1-c**2) + min*(c**2)
pages_fetched = max - max*c**2 + min*(c**2)
pages_fetched = max + min*(c**2) - max*c**2
pages_fetched = max + c**2 * (min-max)
I'm not sure if there's a reason why it's written like that, but (min-max)
looks odd, so I wrote it like:
pages_fetched = max - c**2 * (max-min)
I agree min-max looks odd. max - c**2 * (max-min) looks a bit odd too,
though. Whatever we do here, though, I'd suggest that we keep it
consistent with cost_index().
Other than that, and a quick pgdindent run, this seems ready to me. I'll
mark it as Ready for Committer.
- Heikki
