Re: [Geoserver-users] Filter for a postgis featureType: WFS vs WMS

[Saul F. <Sau...@st...>]

Also, one way to make this faster, Alex, would be create a view based on
your query.  Then simply call for the view in the getmap, rather than
the source table.

Of course, this will only work if there are a small number of values for
the discriminating attribute in your query, since you don't want to
create 500 views or something.

--saul

On Tue, 2005-10-25 at 23:46 -0400, db...@op... wrote:
> Alex,
> 
> 1. The error your report looks like a bug.  Is there any more
> information in the log?  How much memory are you giving to Geoserver?
> 
> 2. The way WMS and WFS handle <filters> are different.
> 
>    For WFS, they do what you want them to do -- they always pass the
> filter off to the datastore. That means it gets converted into the SQL
> WHERE clause.
> 
>    For WMS, it handles <filters> differently because there could be
> multiple filters and else clause (they renderer features that were not
> caught by any of the other rules).
> 
>    So, it makes a request for all the features that intersect the view
> rectangle.  It also makes a set of Rules that are valid for the current
> scale range.  The main loop looks like this:
> 
>      For each Feature in the view rectangle (Datastore processes this)
>          For each Rule (all handled by java)
>               IF the Feature satisfies the <Filter> render it
>          If no Rules were 'hit', then render with the <Else> rule
> 
>   One of the ways of speeding this up will be (if there are no ELSE
> rules or empty-filter rules) to <Or> together all the filters and send
> that off to the Datastore.  For datastores like PostGIS, this will be
> quick if there are only a FEW features in the view box are rendered
> (ie. only show highways in a giant roads dataset).  If most features
> are rendered (ie. show all the roads in a road dataset) it will be a
> bit slower because it is processing each filter twice -- once by the
> datastore and once by the <Rule> processor.
> 
> I've been thinking about doing this for a long time, but most people
> tend to render most of the features, so its not actually going to make
> this faster for most people.  In fact, its likely to make things a
> little slower.
> 
> I'll ask the geotools people about it,
> 
> dave
> 
> 
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