[mapguide-users] Speeding up map rendering

[Kenneth Skovhede, GEOGRAF A/S]

Hi Traian.

I am primarily using the OGR provider with MI-TAB data. I have also seen 
the slowdown with SDF files (which is probably because it uses SQLite).

I like the idea you have outlined, but in case the item is themed, this 
will probably not provide much speedup.

I realize that the general solution is difficult to implement in the 
render, without too much parsing overhead. That is why I am looking for 
a quick fix. Removing all columns is both a huge task, and requires 
copies of data, which again requires syncronization.

If it was a database, a view would be usefull, and since the feature 
schema extensions are like views, I figured it might work.

When the select is performed on a feature source with a schema 
extension, does the render send the name of the extension into the 
select, or does it always query the underlying datasource directly?

Regards, Kenneth Skovhede, GEOGRAF A/S



Traian Stanev skrev:
> Hi Kenneth,
>
> The renderer will unfortunately not respect this -- it always passes an empty property list to FDO, which means select all columns.
>
> Selecting the right columns from the renderer is difficult in general, since one would have to go over all the styles and parse any style expressions to look for property names.
>
> Selecting all columns does not have much of an overhead for some providers. Which provider are you using (it was not clear to me from the ticket description)?
>
> Interestingly, for the SQLite provider, I had the problem of selecting many columns slowing it down a lot and what I did was in case of empty select list, return just the ID and geometry columns. If the client then attempts to read other columns, I reissue the select with additional columns (not this is done once for the feature reader, not per feature). This way I did not have to worry about the client selecting the right columns, and got a reasonable speedup in most cases (of course it is no help if you are actually reading all properties).
>
>
> Traian
>
>
>   
>> -----Original Message-----
>> From: mapguide-users-bounces at lists.osgeo.org [mailto:mapguide-users-
>> bounces at lists.osgeo.org] On Behalf Of Kenneth Skovhede, GEOGRAF A/S
>> Sent: Monday, May 19, 2008 8:20 AM
>> To: MapGuide Users Mail List
>> Subject: [mapguide-users] Speeding up map rendering
>>
>> I have entered an optimization request some time ago:
>> https://trac.osgeo.org/mapguide/ticket/272
>>
>> The problem is that the renderer selects all columns from the
>> datasource, even though only a few (if any) are used.
>> While the general solution might be a bit hard to construct, I have
>> another idea.
>>
>> If I manually add a configuration document/schema with only the desired
>> columns, will the renderer respect this?
>> Does configuration documents (like the one for ODBC) work for all
>> providers?
>>
>> --
>> Regards, Kenneth Skovhede, GEOGRAF A/S
>>
>>
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