Re: Why do indexes and sorts use the database collation?

Hi,

On 2023-11-14 00:02:13 +0100, Tomas Vondra wrote:
> On 11/13/23 23:12, Andres Freund wrote:
> > On 2023-11-13 22:36:24 +0100, Tomas Vondra wrote:
> >> ISTM it's about how complex the rules implemented by the collation are,
> >> so I agree the cost should be a feature of collations not providers.
> > 
> > I'm not sure analysing the complexity in detail is worth it. ISTM there's a
> > few "levels" of costliness:
> > 
> > 1) memcmp() suffices
> > 2) can safely use strxfrm() (i.e. ICU), possibly limited to when we sort
> > 3) deterministic collations
> > 4) non-deterministic collations
> > 
> > I'm sure there are graduations, particularly within 3), but I'm not sure it's
> > realistic / worthwhile to go to that detail. I think a cost model like the
> > above would provide enough detail to make better decisions than today...
> > 
> 
> I'm not saying we have to analyze the complexity of the rules. I was
> simply agreeing with you that the "cost" should be associated with
> individual collations, not the providers.

Just to be clear, I didn't intend to contradict you or anything - I was just
outlining my initial thoughts of how we could model the costs.

Greetings,

Andres Freund