Performance of Scanning a Quadtree Index

[Daniel Morissette]

Brock Anderson wrote:
> 
> I then make a simple WMS request to fetch exactly 1000 features (limited 
> by a bbox) from the layer.  Mapserver take about 500ms. Seems a bit high.
> Geoserver can draw the exact same data, using the *same .qix* index in 
> about 150ms.  Naturally I made every effort to keep the comparison 
> fair.  No reprojection in either case, nearly identical styling, etc.
> 

Ouch! That's no good. Have you verified that MapServer indeed finds the 
.qix and uses it (perhaps by removing the file and seeing that it then 
takes several seconds to render the map)?

> As a further comparison I noticed that Mapserver and Geoserver are 
> nearly equal for fetching/drawing 1000 features from a smaller data set 
> of just 10,000.  Response time there is more like 120ms.
> So on large shapefile data sets Geoserver's index scanning seems to be 
> substantially faster.  Are there any map file options that might improve 
> performance?  Could it be that Geoserver simply has a faster 
> implementation for traversing the quadtree?
> 

Could be. In which case we should compare the two implementations to 
figure what GeoServer does better, and fix MapServer.

Could you please file a ticket about this with the info that was in your 
email? Are you able to share the dataset that you use to reproduce this? 
Also, if you can include a link to the GeoServer source file(s) that 
handles the .qix reading in the ticket so that we know where to look to 
compare the two implementations then that would be great. I will not 
have time to look at this before 5.0 is released, but maybe someone else 
will... or at a minimum we need to make sure we try to address this in 5.2.

Thanks

Daniel
-- 
Daniel Morissette
http://www.mapgears.com/