[gdal-dev] Understanding VSI caching

[Andrea Aime]

On Mon, Apr 9, 2018 at 6:43 PM, Even Rouault <even.rouault at spatialys.com>
wrote:

> Hi Andrea,
>
> Are you speaking about the cache machanism enabled with the VSI_CACHE=YES
> env variable ?
>

I read there was some caching, but was not that specific. So, memory
caching is there, it's per file,
but not enabled by default, while disk caching is there, global, and
enabled by default?


> If so that's described at
> http://gdal.org/gdal_virtual_file_systems.html#gdal_
> virtual_file_systems_vsicache
> I see it lacks a bit high level details, like specifying this is RAM only,
> and not disk cached.
> I'm going to add some words about that
>
> Otherwise, the full "documentation" :-) is at:
> https://github.com/OSGeo/gdal/blob/master/gdal/port/cpl_vsil_cache.cpp


Hehehe :-)


> The /vsicurl/ and related network file systems have also their own RAM
> cache mechanism
> described at
> http://gdal.org/gdal_virtual_file_systems.html#gdal_
> virtual_file_systems_vsicurl


The "detect sequential reading" part is interesting, if I'm not mistaken
the logic is here,
right?

https://github.com/OSGeo/gdal/blob/master/gdal/port/cpl_vsil_curl.cpp#L1845

Thanks a lot for the useful information, as usual :-)

Cheers
Andrea


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