[postgis-devel] GeomUnion Performance Info

[Bill Binko]

On Wed, 22 Jun 2005, Bill Binko wrote:
> > 
> > > BTW: I tried to create a btree index on my parcels, but got this:
> > > 
> > > gis=# create index parcel_shape_btree ON parcels (parcel_shape);
> > > ERROR:  index row requires 8452 bytes, maximum size is 8191
> > > 
> > > go figure.
> > 
> > Ach! I think we should visually see that btree order!
> > Can you avoid clustering and just use ORDER BY ?
> > 
> > Actually... first thing would be evaluating difference
> > between the two (GiST and btree) in terms of performance.
> 
> I have figured out a way to get this: it is running now.  I will post when 
> it's done.

It's done.  BTW: you need to login twice (same username/password) due to 
my stupidity -- sorry.

What I've found is that they are VERY VERY similar.  In fact, I thought 
you were wrong, and that, in fact the gist had been used for Order By.  
However, when you soom in, you can see that the Order By allows some 
shapes to be drawn early (black dots in the white areas) where as the gist 
ordering seems to be more consistent.

Bill