[Mapserver-users] Mapserver WFS performance

[Frank Warmerdam]

Yewondwossen Assefa wrote:
> Here is how things work :
>   - the user does a wfs request
>   - in is translated in mapserver query : the query does not take into 
> account the maxfeatures.
>    - The MAXFEATURES is taken into account when generating the 
> resulting   gml file
> 
>   So yes, It ends up doing the query on all the shapes in your case.
> 
>  I think we should modify mapserver low level query functions to be able 
> to pass a maxfeature parameter. Some of the query functions have a mode 
> (single or mulitple), and this notion should be extended to support a 
> maxfeature. Once this is done the wfs interface can take advantage of it.

Assefa, and others,

On a vaguely related note, the current query interface seems to make a
pass generating the 'item ids' for all the features which match the
query.  Then when the query is returned another pass is made fetching the
shapes by id.  With shapefiles this isn't particularly expensive, though it
does presumably result in the features being parsed from the binary twice.

But for some OGR supported formats fetching "by id" can be very expensive.

If we are restructuring the query mechanism what are the chances of reviewing
this whole two pass approach?  Since WFS is basically always using the
query mechanism it seems this is a significant performance issue for some
WFS setups.  Even for "good formats" there is a bunch of overhead.

Of course, I may be mis-understanding how things are working ... I've only
glanced at it.

Best regards,

-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent