mapserver speed issues

[John Spotten]

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-------------------------------------------------

Thanks Frank,

I assume that full use is made of the attribute indexing in native shape files.

bye for now
john

John Spotten
Transport Modeller/GIS Developer
Directorate of Transport, Roads and Stormwater
City of Cape Town
Tel : +27 21 4067325
Fax : +27 21 4186989
Cell : +27 846678901
Email : john.spotten at capetown.gov.za
Web : www.capetown.gov.za


-----Original Message-----
From: Frank Warmerdam [mailto:fwarmerdam at gmail.com]
Sent: 09 February 2005 10:09 PM
To: John Spotten
Cc: MAPSERVER-USERS at lists.umn.edu
Subject: Re: [UMN_MAPSERVER-USERS] mapserver speed issues


 On Wed, 9 Feb 2005 17:55:45 +0200, John Spotten
<John.Spotten at capetown.gov.za> wrote:
> hi ,
>
> does mapserver make use of indexing present in external databases such as
> mapinfo, as I am considering breaking up a 90000 record layer into 5 classes
>  each with it's own styling and doing some further joining with other
> sources.

John,

OGR currently has no support for using mapinfo attribute index, even
though I (ironically) use mapinfo style attribute indexes for Shapefiles
in OGR. 

In any event, it can be very hard to get MapServer to use OGR for
attribute queries.  On recently (in 4.5) was an option implemented in
MapServer to pass the FILTER directive down to OGR.   And even
now classification expressions are always evaluated by MapServer.

So, the situation for attribute query and classification is that you should
really try and do any subsetting you can of data as a preprocessing
step when working with mapserver through OGR.  The situation is
somewhat better with the RDBMS connectors in that you can
provide SQL FILTERs that are evaluated by the database (though
classification is still done in MapServer).

The other kind of index is a spatial index.  OGR and MapServer will
indeed take full advantage of a mapinfo tab spatial index to quickly
extract the features of a small area from a large file.   Only a few
other OGR format drivers support fast spatial searching.

> I know I will have to check speeds over our intranet first for various
> options and log test results.
>
> Is there any documentation on speed issues and tips and tricks on how to
> improve speed.

Nothing terribly organized I am afraid.   For OGR drivers it can sometimes
be helpful to read the driver/format information page on the ogr web site.

Best regards,
--
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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