[OGR] STYLEITEM AUTO performance issue?

[dmorissette]

We should do some performance tests comparing time to render mapinfo data using 
STYLEITEM AUTO vs using similar styles in static classes.

Here is the initial problem report and my reply:

----------

"Lars V. Nielsen" wrote:
> 
> Can you verify that using STYLEITEM AUTO on large MapInfo vector tables will 
slow down the
rendering considerably ?
> 
> I'm rendering some 20 layers, and experience response times of 5+ seconds.
> When I instead set a specific class definition per layer, it redraws in 1-2 
seconds.
> 
> Is this due to the interpretary nature of the style fetching in OGR/MITab ?
> 

Lars,

It is normal to notice a performance difference when using STYLEITEM
AUTO since MapServer has to parse the style string and generate CLASSes
on the fly for every object.  However you report that it takes more than
twice the time and I find that a bit slow.  Hopefully you are comparing
performance based on the same style in both cases.  I mean if the
STYLEITEM AUTO was producing 5 pixel lines with polygon fills, etc then
make sure that you compare with the same type of styles when using
static CLASSes.  I just want to rule out the possibility that the
difference could be due to the fact that the features use fancier styles
with STYLEITEM AUTO.

[dmorissette]

Enhancement for 4.1 - performance tuning of STYLEITEM AUTO