[postgis-devel] GeomUnion Performance Info

[strk at refractions.net]

On Wed, Jun 22, 2005 at 05:19:01PM -0400, Bill Binko wrote:
> 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.

Similar in terms of performances also or just visual effect ?
Did you try the short-circuit tests ? Would you add curves
for them as well if you do ?

--strk;