[Qgis-user] Readonly gpkg

[Greg Troxel]

Jürgen E. Fischer <jef at norbit.de> writes:

> On Tue, 11. Jan 2022 at 09:10:57 -0500, pergler at gmail.com wrote:
>> I've tried making the gpkg read-only, which hasn't crashed anything in brief
>> testing and generates no warnings. However, it feels risky, and clearly QGIS
>> or OGR aren't fully happy, since the temporary shm and wal files don't get
>> deleted on exit. So I'm hesitant to continue doing this for fear of a crash
>> when I'm actually doing something useful.
>
> We do the same with world_map.gpkg - see
> https://github.com/qgis/QGIS/issues/35383.

I had seen that (NetBSD 9, pkgsrc, qgis 3.16.x) and wondered if it was a
packaging error I should look into.  Now I understand.   I have long
found it problematic that the wal/shm files exist and persist for long
periods, and that gpkd files I don't intend to change are modified at
the OS level.

It strikes me that the basic bug needs one of two things:

  1) The geopackage driver should have a read-only access mode, and qgis
  should start out that way, trying to change to read/write only when
  the user hits the edit button on one of the layers.  And, if the file
  is read only, there should be a nice error like "can't make this layer
  writable" and the toggle to write should fail.

  With this option, there perhaps needs to be some kind of lock outside
  of sqlite, which can be multireader and single writer.

  2) somehow, the geopackage layer could hide all this and logically open
  the layer read/write, but refrain from writing to the filesystem.
  Then, when there is an actual write, the db open-for-write can
  happen.   After the database is written, if no layers [are
  editable]or[have unwrittend changes] for some period of time (5m?) the
  database should be changed back to read only.   This is sort of like 1
  but at the gdal layer vs the qgis layer.


Because of this I'm starting to think about moving all my data into
postgis, and not use geopackages any more.

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