Re: Need theory/comprehension help on Multi-Column indexes

Tom, Merlin,

> It's not fundamentally different from single-column indexes.  The only
> aspect of a btree index that requires any knowledge about the content of
> index entries is the "compare two index entries for lesser, equal, or
> greater" operation.  For that, we just compare the first columns, then
> compare the second columns if the first are equal, etc.  Plain
> lexicographic sort semantics.

So the different columns of the index don't have seperate data pages?   It's 
just a partitioned index node?

Wow, no wonder I couldn't figure it out, I was looking for something more 
complicated ...

BTW, while we're on the optimizer, what is random_page_cost supposed to 
represent, exactly?    I used to think it was the ratio of index page 
retreivals to direct page retrievals, but I see that that's already being 
calculated for.    I'm wondering if it might be possible to calculate RPC and 
eliminate it as a GUC.

-- 
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco