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

[Michael Schulz]

Hi,

thanks for the response, see inline ...

2010/6/25  <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.

sorry, I forgot that. I'm using plain mapserver cgi on a linux/debian system.

> 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.

That is an interesting thought. I'll try to examine the returned
packets from the remote wfs server. However, I have several
installations on various servers, with exactly the same setup (well,
running in vm's on different hosts, but the guest system is identical)
and I think the problem is only occurring on "slower" machines.

But thanks, for this pointer. I'll check that.

Cheers, Michael



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