[Qgis-developer] Postgis-Provider and compression

[Pirmin Kalberer]

Hi Andreas,

Am Montag, 9. August 2010, um 14.29:12 schrieb Andreas Neumann:
> Hi all,
> 
> I wonder if the current Postgis-Provider somehow supports or would support
> compression during data-transfer between the QGIS-client and the remote
> Postgis-server. In my experience, data transfer across slower connection
> (DSL, cable) is often rather slow.
> 
> Would there be, technically, a way to accelerate data transfer over slower
> network connections?

I don't know a built-in method for compressing data transfer on Postgres 
connections (http://www.postgresql.org/docs/current/static/libpq-
connect.html).
But you could tunnel the connection e.g. with netcat or ssh (without 
encryption) and compress it with gzip. Other solutions would be a compressed 
geometry format (like http://www.gaia-gis.it/spatialite-2.4.0/) or a partial 
update method. Both would need changes or custom stored procedures within 
Postgis.
A different approach would be using an "offline" database and synchronizing with 
the master database. (We're currently working on this approach in a customer 
project).

> 
> I also remember that Sandro Santilli once suggested a keyword substitution
> parameter for the psql provider so one could use simplify based on map
> resolution/map scale. This should also help to speed up data transfer on
> slower connections
> (http://lists.osgeo.org/pipermail/qgis-developer/2010-May/009923.html) -
> unfortunately noone answered to his mail. I think the proposal would be
> interesting to follow.

You're asking for something like http://tinyurl.com/pgvar I think. QGIS could 
provide useful variables (like :scale) and offer a possibility to configure the 
select statements.
Another way to achieve this could be using custom variables like in
http://www.pgsql.cz/index.php/PostgreSQL_SQL_Tricks#Any_other_session_variables 

Regards
Pirmin


-- 
Pirmin Kalberer
Sourcepole  -  Linux & Open Source Solutions
http://www.sourcepole.com