[gdal-dev] Block cache and VRT sources

[Sean Gillies]

Even,

Does the shared attribute of a VRT sourceFilename element not affect
caching at all? Is the cache avoided so that potentially stale data isn't
propagated, or for other reasons?

On Fri, Apr 19, 2024 at 9:09 AM Even Rouault <even.rouault at spatialys.com>
wrote:

> Sean,
>
> Within a given GDALDataset opened on a VRT, if the VRT references several
> times the same source, only one GDALDataset will be opened for it, so you
> may benefit from the block cache mechanism (if it is triggered.
> VRTSource::IRasterIO() calls IRasterIO() on the source band, which doesn't
> necessarily always trigger block-based reading).  But if you open another
> VRT (or the same one), it will not share the same GDALDataset for sources
> that may be common with the first one, so no re-use of existing block
> cache. For network sources, the I/O cache at the /vsicurl/ level works
> however on filenames, not VSIFILE* instances, so you will save network reads
>
> Even
> Le 19/04/2024 à 16:48, Sean Gillies via gdal-dev a écrit :
>
> Happy Friday, folks!
>
> Are the source rasters of a VRT added to the block cache such that
> different VRTs using the same source can avoid reads from disk or the
> network? Or is it intended that the VSI cache covers this need instead?
>
> Thanks,
>
>

-- 
Sean Gillies
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