[Qgis-user] GeoPackage deadlocks (Andrea Peri)

[Jonathan Moules]

Hi Jarosław,

 > Does the same apply if we only read data from geopackage (not 
overwrite/edit it) on NFS? I have a situation with deadlocks when 
several users are only trying to read data (without competitive writing).

At the file level for SQLite itself, there are basically no constraints 
for reading as far as I know. You can have an effectively infinite 
number of readers (or however many your filesystem allow to access a 
single file at a time). Per the When to use page 
(https://www.sqlite.org/whentouse.html) (my bold):

"High Concurrency

*SQLite supports an unlimited number of simultaneous readers*, but it 
will only allow one writer at any instant in time. For many situations, 
this is not a problem. Writers queue up. Each application does its 
database work quickly and moves on, and no lock lasts for more than a 
few dozen milliseconds. But there are some applications that require 
more concurrency, and those applications may need to seek a different 
solution."

I would suggest your situation is a QGIS/GeoPackage-driver bug/limitation.

Cheers,

Jonathan


On 2019-10-07 15:46, jaroslaw.sadowski at cpk.pl wrote:
> Hi everybody,
>
>   
>
> Very interesting thread…
>
> Does the same apply if we only read data from geopackage (not overwrite/edit it) on NFS? I have a situation with deadlocks when several users are only trying to read data (without competitive writing).
>
> Can anyone confirm this with his case?
>
>   
>
> greeting from Poland
>
> Jarosław Sadowski
>
>   
>
> From: Qgis-user <qgis-user-bounces at lists.osgeo.org> On Behalf Of Jonathan Moules
> Sent: Monday, October 7, 2019 4:17 PM
> To: Tobias Wendorff <tobias.wendorff at tu-dortmund.de>; Andrea Peri <aperi2007 at gmail.com>
> Cc: qgis-user <qgis-user at lists.osgeo.org>; Paul Wittle <paul.wittle at dorsetcouncil.gov.uk>
> Subject: Re: [Qgis-user] GeoPackage deadlocks (Andrea Peri)
>
>   
>
> (A little late).
>
> TL;DR: at least for QGIS, is - never multi-user edit SQLite/SpatiaLite/GeoPackages on network file systems.
>
> SQLite, (and therefore SpatiaLite and GeoPackage) has quite a few caveats when it comes to multiple users trying to edit it at once.
>
> https://www2.sqlite.org/howtocorrupt.html
>
> (my bold)
>
> "SQLite depends on the underlying filesystem to do locking as the documentation says it will. But some filesystems contain bugs in their locking logic such that the locks do not always behave as advertised. This is especially true of network filesystems and NFS in particular. If SQLite is used on a filesystem where the locking primitives contain bugs, and if two or more threads or processes try to access the same database at the same time, then database corruption might result."
>
> And there's also:
>
> https://www.sqlite.org/whentouse.html
>
> Put simply (Note: I'm not an expert): It's fine to edit SQLite databases if they're not on a network file system with as many users as you want, or if they are on a network and you can guarantee only one process is going to write. However if multiple people/processes want to write to a network file system, you'll need a piece of middleware to manage the process, otherwise there's a good chance of corruption as Paul is seeing.
>
> It may also be that QGIS is doing some of the other things on the "how to corrupt" page too. I imagine it will only get worse if you use multiple different software packages to edit simultaneously.
>
> Cheers,
>
> Jonathan
>
> On 2019-09-27 09:50, Tobias Wendorff wrote:
>
> Am 27.09.2019 um 10:24 schrieb Andrea Peri  <mailto:aperi2007 at gmail.com> <aperi2007 at gmail.com>:
>   
> Have you tried to use spatialite instead of geopackage. ?
>
>   
> Why not plain SQLite? Nobody needs and uses the spatial functions of Spatialite, they are even not part of bloatware GPKG (sorry, the created db-files are huge without any compression).
>   
> The only reason is indexing and this could be forked off GPGK and Spatialite.
>   
> To the topic: I think, it‘s always a bad idea to let multiple users work on a single SQLite-based database. It hasn‘t been created for this reason.
>
>
>
>
>
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