[mapserver-users] Tiled PNG doesn't work for WCS (and WMS)

[Frank Warmerdam]

Charlton Galvarino wrote:
> Hi, Frank.
> 
>> I believe much of the performance problem is that some versions of 
>> GDALOpen() do a scan of the whole directory as part of the file opening 
>> process. In a directory, like Steven's, with 60000 tiles (120000 files!) 
>> that becomes a significant performance problem.  I have suggested a 
>> configuration item that might disable this depending on his version of 
>> GDAL.
> 
> That got my attention!
> 
> In one dir say I have 20k .png images.  In that same dir I have 400 .shp
> tileindexes which point to them.  I.e. each tileindex points to 50 of those
> .png's.  Are you saying that when I send a MS viz request based on a
> specific tileindex .shp, I could be scanning the whole dir (depending on my
> version of gdal)?

Charlton,

Yes, for each GDALOpen() request.  So for each actual raster file which we
attempt to open.

I would add some other aspects of operating systems may respond poorly to
very large directories so it is a common practice to break down tiling
systems into a heirarchy (like the google tile tree).

I'm not saying your configuration can't be fast, but you are playing with
fire if performance is the goal.

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    | Geospatial Programmer for Rent