[mapserver-dev] Call for discussion on MS RFC 114: Faster retrieval of shape count

Wed Feb 10 03:52:54 PST 2016

Hi,

I am thinking about the metadata setting “wfs_ignore_maxfeatures_for_hits”. While it is certainly useful for the users sometimes I believe that ignoring maxfeatures is still not WFS standard compliant. Quotation from WFS 1.1.0 standard: 

"In this way  [by using resultType=hits] a client may obtain a count of the number of features that a query would return without having to incur the cost of transmitting the entire result set."

If ignore maxfeatures is set in the metadata it makes that WFS service permanently non-compliant. I wonder if we could have a vendor parameter like "&feature_count=total" for controlling which count &resultType=hits will return.  For end user both counts can be valuable: total count for knowing the size of the layer and the count that takes maxFeatures into account the maximum size that can be used for paging.

-Jukka Rahkonen-

Even Rouault wrote:

> Hi Steve,

>> Hi Even: I take it that "the_normal_sql_query" could also include the 
>> translated filter described by a layers FILTER/FILTERITEM combo or the 
>> NATIVE_FILTER processing option, correct?

> Hum, I was convinced that my implementation in the PostGIS driver already did that, but it didn't ! And by further checking, I also saw I missed that
msQueryByFilter() could be called indirectly by the WFS code through FLTxxxxx().

> Those 2 issues are now fixed with :
https://github.com/rouault/mapserver/commit/4557afed33f92d22c969282d22dacf027e5e7387
https://github.com/rouault/mapserver/commit/28354fe4bd5f5c3058a87ebc31d55ca7905388f3

> I've also added new test cases in msautotest:
https://github.com/mapserver/msautotest/commit/05e8264ce737a795d81f1a87614fa5c87399de91

> 
>> The only other gotcha is how (or if) to deal with class-level templates.
>> The presence of a template is used to decide if a feature is to be 
>>processed as part of query operation and, in theory, if it should be 
>> counted. Typically one would configure a template at the LAYER-level 
>> but it's also possible to define CLASS-level templates. For example:
>> 
> CLASSITEM 'column'
>> CLASS
>>   EXRESSION 'foo'
>>   TEMPLATE 'void'
>>   ...
>> END
>> CLASS
>>   EXRESSION 'bar'
>>   # no template
>>   ...
>> END
>> 
>> In this case you wouldn't know if you should count a feature until you 
>> know what CLASS it is. Granted this is an older configuration option 
>> that probably isn't widely used but it does exist. Perhaps it's 
>> currently broken anyway, I haven't tested. Just not sure how to deal with it.
>> Perhaps it just needs to be noted as a configuration exception folks 
>> need to avoid when setting up WFS. I'd be happy to see that option 
>> removed in the next version - it adds unnecessary complexity to the 
>> query code. You can see the affect in msIsLayerQueryable() in 
>> mapquery.c  among other places in that source file.

> I indeed see such stuff in msQueryByRect() and didn't know what it was supposed to do. In fact, the WFS code has always forced a dummy "ttt.html" layer template (if no layer template is defined), so class templates are de-facto unused in WFS (since the msQueryXXXX() functions do no test class templates if a layer template is defined). And the msLayerGetShapeCount() optimization path is only taken if a layer template is defined. So for non-WFS case, map-
>query.only_cache_result_count == 1 and class templates will still work 
>as
before.

> I've modified the RFC with the above changes and precisions :
https://github.com/mapserver/docs/commit/76dfe8cb73c9c3de2f2e878e7c856dedc7a10c28

> Thanks a lot for your very much appreciated input !

> Unrelated note: my latest commit fails in renderers/wmsclient.map because
http://demo.mapserver.org/cgi-
bin/mapserv?map=/osgeo/mapserver/msautotest/world/world.map&service=WMS&request=GetCapabilities
doesn't respond.

> Even

>> 
>> Steve
> 
> -----Original Message-----
> From: mapserver-dev [mailto:mapserver-dev-bounces at lists.osgeo.org] On 
> Behalf Of Even Rouault Sent: Monday, February 08, 2016 4:58 AM
> To: MapServer Dev Mailing List <mapserver-dev at lists.osgeo.org>
> Subject: [mapserver-dev] Call for discussion on MS RFC 114: Faster 
> retrieval of shape count
> 
> Hi,
> 
> Your comments on the following RFC are welcome :
> http://mapserver.org/development/rfc/ms-rfc-114.html
> 
> Even

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