[mapguide-internals] Raster provider problems...

[Frank Warmerdam]

Robert Bray wrote:
> Hmm,
> 
> Introducing this is a good thing. The resolution is to single thread the 
> GDAL provider (and any other provider that supports less than per 
> connection threaded) to prevent the server from crashing under load.

Robert,

Are you suggesting that the resolution is for Mapguide to limit use
of fdogdal to a single thread?  I would agree that is an appropriate
solution (as long as it returns that it is single threaded).   I have/had
the impression that MapGuide had just taken on a policy to not ever
utilize single threaded providers.

> really have no choice. To be honest, I am surprised that users using the 
> GDAL provider have not complained of problems or maybe this is the 
> source of some of the stability issues and we just have not caught it 
> because we did not protect the server from non thread safe providers.

Well, in the case of GDAL it can't guarantee correct multithreaded operation.
For instance, most format drivers have not been vetted for thread safety
issues, and I'm sure that at least a few have them.

And at the point that the provider is asked about thread safety the
provider doesn't know anything about what format drivers it will be using
(I think).

I will note that GDAL is threadsafe under certain restricted circumstances:

  o Using only threadsafe vetted drivers (ie. GeoTIFF, HFA).
  o Only having a single thread touch any given GDALDataset at any
    one time.

Best regards,
-- 
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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    | President OSGeo, http://osgeo.org