[Mapserver-users] Mapserver WFS performance

[Yewondwossen Assefa]

I have added 2 enhencements bugs (552 and 553) to keep track of these 
discussions.

Later,


Frank Warmerdam wrote:

> 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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Assefa Yewondwossen
Software Analyst

Email: assefa at dmsolutions.ca
http://www.dmsolutions.ca/

Phone: (613) 565-5056 (ext 14)
Fax:   (613) 565-0925
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