[mapserver-users] Can similar, nearly simultaenous requests disturb mapserver?

[christopher.schmidt at nokia.com]

On Jun 25, 2010, at 10:14 AM, ext Michael Schulz wrote:

> Hi all,
> 
> I have a slightly strange problem and would like some thoughts of the experts.
> 
> I have a mapfile, that serves one layer that is connected to a wfs
> datasource (aka wfs client layer) as a wms layer. I have the problem
> that when doing two similar requests at nearly the same time, very
> often one request throws an error. Interestingly not always the same.
> In descending number of appearances:
> 
> - "msDrawMap(): Image handling error. Failed to draw layer named  ...
> msWFSLayerWhichShapes(): WFS connection error. WFS request produced no
> oputput for layer".
> - "msOGRLayerInitItemInfo(): OGR error. Invalid Field name: TYPE"
> - "msOGRFileNextShape(): OGR error. XML Parsing Error: The input ended
> before all started tags were ended. Last tag started was
> 'gml:coordinates'"
> 
> The other request is always drawn correctly. To me it seems as if the
> downloaded gml-File is somehow shared between both requests, only
> allowing the "first" request to parse it correctly and to draw a map.
> 
> I have reproduced this error with several mapserver versions, ranging
> from 5.2 up to 5.6.

You didn't mention how you have MapServer configured; is it as a CGI,
via FastCGI, something else? In general, running mapserver + GDAL in a
threaded environment may have some side effects, depending on how you're
using them, so if you're using FastCGI + threads somehow, that could be
bad.

If you're not doing this, then I would argue this really sounds like a 
problem on the server you're connecting to; you might want to get a 
packet dump of the outgoing HTTP requests during this time, and see
if you can determine what the server is returning. If you've been
using the same backend server, the problem may well not be 
MapServer.

Regards,
-- 
Christopher Schmidt
Nokia