[QGIS-Developer] QGIS/OGR: FeatureIds reassigned on write to data provider?

[Sandro Mani]

On 10.07.2017 13:58, Even Rouault wrote:
>
> > I did some playing around and came up with some FeatureId mapping code
>
> > which is pretty space efficient (basically requiring just
>
> > 3*nDeletedFeatures entries), see below.
>
> >
>
> > The code however assumes that the gaps in the fid-sequence are filled by
>
> > decreasing the fids after the gap, which may be pretty specific to the
>
> > OGR/Shapefile behaviour.
>
> This should clearly be restricted to Shapefiles. Other drivers don't 
> have this compaction logic and will let happily holes in the feature ids.
>
> > Hence in my view such code should really belong
>
> > into the OGR provider (or perhaps even ogr itself) and not in the
>
> > plugin. Thoughts?
>
> Regarding putting that in OGR itself, there's no such API for that 
> right now, and I'm not completely clear of the value to add one 
> (specific use case, for a single driver)
>
> Perhaps the QGIS OGR provider would be a better place for now.
>
So that kinda works, but repacking still causes dreadful performance 
(say after fixing a couple of hundred "minimal area" errors, which 
results in the small features getting deleted, the shapefile is repacked 
after every delete).

So I'd really need a way to freeze repacking, even just for the timespan 
the plugin is busy fixing the errors. Unless there are some better 
ideas, I'll look at adding corresponding methods. A cool name would be 
beginTransaction/endTransaction which is kinda generic and could make 
sense for other providers as well, but unfortunately it collides with 
the existing transaction logic (QgsTransaction) which is about 
multi-layer transaction groups...


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