RfD: Support for layer specific resources

[Bernhard Reiter]

On Fri, Apr 16, 2004 at 07:38:27AM +0200, Martin Schulze wrote:
> Bernhard Reiter wrote:
> > On Thu, Apr 15, 2004 at 08:20:50PM +0200, Martin Schulze wrote:
> > > In the past, Thuban supported mostly local layers.  As a result,
> > > several dialogs were not classified layer-specific and hence
> > > controlled through a general control within Thuban.  This poses a
> > > problem since the general control of Thuban which also creates menus
> > > and legends thinks that all layers are "normal" layers.
> > 
> > Another problem that comes with "remote" layers is buffering.
> 
> Yes.  I've already thought about caching since on a slow line it
> takes a while to retrieve the remote image.
> 
> > We saw that with the postgis tables already, 
> > but I also expect this to be a problem with your layers, too.
> 
> True.
> 
> 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. :)
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