[Qgis-developer] [Qgis-user] Caching remote postgis layers?

[Marco Hugentobler]

Hi Willem

Another thing to explore is the offline editing plugin. It caches 
postgis layers to a local spatialite database and can even be used to 
synchronise edits between local spatialite db and remote postgis db.

 >Sourcepole have developed (for NIWA, New Zealand) a plugin that 
supports local caching of WMS & WFS data sources. This could probably be 
adapted to support other input >formats. Marco Hugentobler did the 
coding for this - he can perhaps comment?

The plugin saves WMS as local rasters and WFS as local vectors. This is 
similar to save as local vector / raster file by hand. However the 
plugin is more convenient because it manages the local storage and the 
reference to the remote uri.  It has some other nice features like 
synchronizing / offlining in a graphical way. Btw., we hope to include 
this plugin (a C++ one) into the main repository after 2.0 feature 
freeze is over.

Regards,
Marco

On 06.08.2013 03:20, Brent Wood wrote:
> Hi Willem,
>
> Why can you not save such a layer or a selection from such a layer, as 
> a local shapefile (or other supported format). is this not effectively 
> a "local cache"? Delete/overwrite when you desire.
>
> Where is the performance bottleneck? Postgis, network, QGIS?  Just 
> creating a local cache will not necessarily speed things up, if your 
> database is on a fast server with a fast network, it may even get slower.
>
> Sourcepole have developed (for NIWA, New Zealand) a plugin that 
> supports local caching of WMS & WFS data sources. This could probably 
> be adapted to support other input formats. Marco Hugentobler did the 
> coding for this - he can perhaps comment?
>
> As Nathan says, caching a local snapshot of a dynamic, multi-user 
> database will result in something that gets out of sybc with the 
> source pretty quickly. Caching a local copy of a largely static 
> database is relatively safe.
>
> Cheers
>
> Brent
> ------------------------------------------------------------------------
> *From:* Nathan Woodrow <madmanwoo at gmail.com>
> *To:* Willem Buitendyk <willem at pcfish.ca>
> *Cc:* qgis-user <qgis-user at lists.osgeo.org>; 
> "qgis-developer at lists.osgeo.org" <qgis-developer at lists.osgeo.org>
> *Sent:* Tuesday, August 6, 2013 11:07 AM
> *Subject:* Re: [Qgis-user] Caching remote postgis layers?
>
> Hey Willem,
>
> I'm not aware of a feature like that.  The best place to ask this 
> question to see if anyone is working, or planning to work, on it is 
> the developer list.  I have copied it in so it show up there too.
>
> Caching could be done by storing the returned results in a memory 
> spatialite database. The tricky thing is knowing when to get any new 
> results from the postgis database when things have changed on the 
> database.  How does Manifold handling viewing an area, updating 
> something using SQL on the database (not though Manifold) and then 
> looking at that area again?
>
> - Nathan
>
>
> On Tue, Aug 6, 2013 at 2:44 AM, Willem Buitendyk <willem at pcfish.ca 
> <mailto:willem at pcfish.ca>> wrote:
>
>     I've noticed looking at the roadmap that caching remote postgis
>     data is not on the list.  I love qgis but a lot of my work
>     involves connecting to a remote postgis database.  The speed of
>     navigating a large dataset is, at the moment, rather unbearable.
>      I also use Manifold GIS and the difference in speed is shocking,
>     presumably because Manifold is caching the dataset.  This seems
>     like it should be a relatively easy thing to implement.  Is there
>     interest on this board for this feature?  I was thinking at taking
>     a stab at contributing to the source code but am wondering about
>     methods to achieve data caching most efficiently.  Look forward to
>     others thoughts?  Or maybe I missing something that is already in
>     place?
>
>     Willem
>
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-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Weberstrasse 5, CH-8004 Zürich, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee

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