[Qgis-developer] [QGIS Server] How to share QgsPostgresSharedData between multiple QGIS instances

[Matthias Kuhn]

On 12/22/2016 05:06 PM, Alessandro Pasotti wrote:
> On Thu, Dec 22, 2016 at 4:10 PM, Matthias Kuhn <matthias at opengis.ch
> <mailto:matthias at opengis.ch>> wrote:
> 
>     Hi Alessandro
> 
>     >
>     > In Lyon we also talked about how to share caches between different
>     > server processes, do you think that the shared memory segment would be
>     > appropriate in that case?
> 
>     What are the caches used for?
> 
> 
> mainly per-project capabilities.
> 
> With QGIS 3 refactoring the QgsProject class will probably hold all the
> information we need instead of parsing the project XML like we are doing
> now, I think that we'll need to cache the QgsProject instance itself if
> we want scalability by spawning multiple server processes without the
> need to re-parse the project file, this in case we need to serve
> multiple projects of course.

Is there some profiling information available about what's the slow part
(parsing, loading of layers, loading of print composers...)?

Saving a whole project including layers etc. in a shared memory sounds
like a challenge.
It's possibly easier to identify which parts are slow and cache them on
some backend.
If this mechanism is abstract enough to work with a file based format
like sqlite or memcached/redis, that would be awesome because QGIS
desktop could also benefit and depolyment on a server will probably be
easier if it does not depend on additional services.