Le lundi 06 février 2012 02:41:40, Etienne Tourigny a écrit : > Hi all, > > The default memory limit for warp operations is 64MB, which is far too > low using recent hardware and leads to inefficiencies in I/O when > warping large images. > > This can be changed using the -wm option of gdalwarp, or if using the > API change the value of GDALWarpOptions::dfWarpMemoryLimit. > More information here: > http://trac.osgeo.org/gdal/wiki/UserDocs/GdalWarp#WillincreasingRAMincrease > thespeedofgdalwarp > > However, it would be better to do both of the following: > > 1) Change the default value of 64 MB to something higher, perhaps > depending on the machine's configuration (say 1/4 of RAM) - this > possibility is mentioned in gdalwarpoperation.cpp .
Finding good default values is quite difficult and somehow arbitrary. There's however something to be aware : in the trac entry you quote above, there's a mention of a use case where more RAM for dfWarpMemoryLimit will actually decrease performance. So if you intend increasing it substantially (which would be the case for 1/4 of RAM on modern configurations), that might make things significantly worse for that use case. That's definitely something to at least benchmark and lilely fix in the warping code. The use case if I remember well is "gdalwarp smallimage bigimage" (the real use case being generally "gdalwarp smallimage1 smallimage2 ... smallimageN bigmosaicofallsmallimages"). If you increase dfWarpMemoryLimit currently, we will currently read an area of bigimage much larger than needed to include the extent of smallimage, which cause excessive read operations before warping, and excessive write afterwards. > 2) Add a config option so that the default can be set for all > operations by the user (which overrides 1, but can be overridden for > each operation) Not sure to understand how option 2) if different from the -wm option and how it would be implemented ... > > > Any comments? > > regards, > Etienne > _______________________________________________ > gdal-dev mailing list > [email protected] > http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/gdal-dev
