I'm not really sure that I want to move
these separate layers into one with just class definitions because the
legend does display the class definitions only layers
That's not right; it should show them for every class that has a NAME
element.
Looking at your code sample, I'd have to agree that there are probably
circumstances where 5 layers using FILTER may be faster than 1 layer
using 5 classes, and vice versa.
If your data were in PostGIS and the filtering were happening by the
same column in each case, and that column were indexed and also
clustered, that'd probably show some excellent performance using the
filter (keep the filtering in the DB instead of taking it to Mapserver).
If your data is in shapefiles, though, the indexing by criteria isn't
happening and Mapserver has to do a sequential scan and class-matching
for every record in the spatial region represented. For each layer. Five
times. Ouch.
So yeah, if you're sticking with shapefiles I'd agree with the others
that 1 layer with 5 classes would probably be the best bet. If you're
willing to put in the work to put it into PostGIS, you could probably
have 5 layers work very nicely.
I'm really wondering if this is a hardware issue. The box is
a Sun server with 4 x 400MHz processors and 4GB ram. That might not be a
powerful enough machine to do what I'm trying to do.
Should be fine; that's plenty of hardware.
You might want to try shp2img on your mapfile as you edit it, to help
make sure your benchmark conditions are consistent between runs.
http://mapserver.gis.umn.edu/docs/reference/utilityreference/shp2img
Good move, Hal. I'll take a note of this and add it to the performance
docs we've been working on.
--
Gregor Mosheh / Greg Allensworth
System Administrator, HostGIS cartographic development & hosting services
http://www.HostGIS.com/
"Remember that no one cares if you can back up,
only if you can restore." - AMANDA
