[QGIS-Developer] Processing: questions on temporary files

[Nyall Dawson]

On Fri, 6 Dec 2019 at 23:19, Matthias Kuhn <matthias at opengis.ch> wrote:
>
> Other proposals are very welcome as well. I don't insist on GeoPackage.
> All I do is being a bit skeptic that rolling our own format will
> magically solve problems that one hundred other formats did not solve :-)
>

The issue is that the memory provider, by design, MUST be a lossless
reflection of all the capabilities offered in QGIS vector layers. That
means support for every geometry type, and field type handled by QGIS.
Geopackage might be capable of that now... but it won't always be, due
to the inherent limitations of that format. (No multi-geometry
support, no mixed CRS geometry support, no support for advanced field
types like range/interval fields, etc).

I don't think it's useful to even think of rolling our own data format
-- that's NOT what's required here. All that we need is a way of
paging the currently in-memory storage of features used by the memory
provider to disk when required. This disk based paging would be
totally temporary (always deleted when the layer is removed), have no
requirement for a stable binary format (we could change the paging
binary structure version by version if needed), and absolutely no need
for ANY other programs to be able to parse or interpret. It's not a
data format at all -- it's just a disk based reflection of what we
currently store in RAM, along with some smart indexing to optimize
access.

Nyall



> Regards
>
> Matthias
>
> >
> > Regards,
> >
> > Richard Duivenvoorde
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