RfD: Support for layer specific resources

[Frank Koormann]

* Bernhard Reiter <bernhard at intevation.de> [040416 12:27]:
> On Fri, Apr 16, 2004 at 07:38:27AM +0200, Martin Schulze wrote:
> > I thought about hooking an image cache into the WMSLayer.GetMapImg().
> > 
> > I've also thought about buffering the current image locally so
> > it doesn't have to be retrieved when the image needs to be rendered
> > again (for hide/unhide for example).
> 
> That is the major point I guess.
> Most redraws will not warrant a new remote fetch.
> Remote fetches are expensive in general,
> especially if the line is slow or the server underload.
> The possibility to keep stuff on the client is very important.
> It must be configuration in cases the client is a smaller machine.
> 
> > > We do not only need layers specific information, 
> > > but also general and layer specific buffering methods.
> > 
> > What kinds of data need to be buffered with postgis tables?
> 
> The problem is the same as above.
> I just do not know on which level of Thuban the caching is best.
> 
> > I'd expect this to be tons of rows from SQL queries.  Is that true?
> 
> It depends, could be.
> We could buffer it later in the processing pipeline.
> But buffering SQL result would be a good start.
> 
> > Anything else that should be buffered/cached in Thuban?
> 
> Probably a lot. :)

Based on the assumption that rendering is the most expensive process step
(at least for local layers) I had in mind to cache each rendered layer 
image separately. Would speed up Thuban significantly as long as the map 
extend is constant, but I haven't thought much about memory requirements 
so far ...

On the other hand analysis on database layers requires also the query
results, so caching these would also be helpful.

Frank

-- 
Frank Koormann                             <frank.koormann at intevation.de>
 Professional Service around Free Software       (http://intevation.net/)
 FreeGIS Project                                 (http://freegis.org/)
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