[Qgis-user] Geopackage slow on NAS if not read-only

[Greg Troxel]

Neil B via QGIS-User <qgis-user at lists.osgeo.org> writes:

> When you open a GPKG, meaning you are accessing data from the file, the
> -wal file and its partner the -shm file are created in the same directory
> as the GPKG file. The WAL file is created to implement atomic commit and
> rollback. At the file system level, if you place the GPKG in read only mode
> then there is never a concern about writing data to the database so the
> -wal and -shm temp files are not created. The behaviour of the temporary
> files has nothing to do whether the layer is put in edit mode or not, but
> is a functionality of SQLite.

I thought that there was an improvement to gdal so that opening a gpkg
layer read only would result in not creating temp files, and they would
only arise when one edited the layer.

I have always viewed situations where logical read operations lead to
filesystem writes as buggy, intrinsically so, but they are very
troublesome for distributed filesystems and version control.

> You don't have the speed problem with shapefiles as they have no mechanism
> to protect them from multiple users and no mechanism to ensure the
> equivalent of an atomic commit. If multiple people make edits to the same
> shapefile, the last one to save is the one that decides what is written,
> assuming the shapefile doesn't get corrupted in the mean time.

That's great perspective!