[mapserver-users] Using Fast CGI with MapServer to alleviate poor performance

[James Perrins]

A couple of issues / tips we have found in this sort of scenario.

1) Edit your epsg file to contain only the projections you want - this
can make a big difference - presumably because its doind a slow string
search each time
2) If using OpenLayers (or google maps etc) - the tiling sends
multiple requests to the WMS server.  If you are using IE in
particular - this restricts you to 2 concurent threads to any one
server - mean9ing that your (say) 16 tile requests can only be
processed 2 at a time.  Firefox has a similar restriction by default -
but you can override it.  You can see this at work using Firefox with
a tool like firebug.

We foun it was much much quicker if you can change yout application to
request a single WMS tile for the whol map rather than individual
256x256 tiles.  Obviously this may have implications if you were
trying to cache tiles etc - but if not its massively quicker

HTH
James

On Wed, Sep 17, 2008 at 4:40 PM, John Westwood <John.Westwood at port.ac.uk> wrote:
> Hi,
>
> I am trying to use fast_cgi with MapServer, specifically mod_fcgid on SLES 10.2.
>
> I have mod_fcgid correctly set up within Apache because it works with another FCGI application (IIPImage).
>
> I have successfully compiled MapServer 5.2 with fast_cgi support. I used this page to help me:
> http://mapserver.gis.umn.edu/docs/howto/fastcgi
>
> However, when I try to use MapServer with mod_fcgid I receive the following error:
>
> The server encountered an internal error and was unable to complete your request
> Error message: Premature end of script headers: mapserv
>
> I am really lost as to what the problem could be; the non fast_cgi version of MapServer that I compiled worked fine. Perhaps it is something to do with setting the LD_LIBRARY_PATH in the mod_fcgid.conf file?
>
> At the moment I have it set as follows:
>
> DefaultInitEnv LD_LIBRARY_PATH "/usr/lib:/usr/local/lib:/usr/lib/postgresql"
>
>
> The reason I am trying to get MapServer to work with fast_cgi is because I am experiencing poor performance with OpenLayers. I believe that OpenLayers starts a new MapServer instance for each tile request, thus causing an unnecessary overhead. Am I correct?
>
> I will also be using Tilecache, but my experiments have also found this to be slow. It is currently set up to use mod_python. The hardware we are running on is a dual quad core (eight cores in total) Xeon . So it shouldn't be slow!
>
> I would greatly appreciate any help on getting MapServer to work with fast_cgi . I would also welcome any comments regarding performance issues with OpenLayers / MapServer / Tilecache .
>
> Thanks very much,
>
> John Westwood
>
> Great Britain Historical GIS Project
>
> _______________________________________________
> mapserver-users mailing list
> mapserver-users at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/mapserver-users
>



-- 
Dr James Perrins
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