Re: Hash indexes

Ühel kenal päeval, T, 2006-08-01 kell 10:54, kirjutas Andrew Dunstan:
> Gregory Stark wrote:
> > 
> > I looked a while back and was suspicious about the actual hash functions too.
> > It seemed like a lot of them were vastly suboptimal. That would mean we're
> > often dealing with mostly empty and mostly full buckets instead of well
> > distributed hash tables.
> >
> >
> >   
> 
> This is now sounding like a lot of low hanging fruit ... highly 
> performant hash indexed tables could possibly be a very big win.
> 

Are you sure about the badness of our hash functions ?

I just tested and hashtext(text) has about 1.4% of collisions on about
120M distinct texts, which is not bad considering thet total space for
hashes is 4G, meaning that 120M covers itself already 3% of possible
hash space.


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