Hi Pirmin,
Thank you for your thoughts on the issue. My comments inline.
On 08/09/2010 10:47 PM, Pirmin Kalberer wrote:
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).
ok - that's what I thought. So the best solution would be probably to
get the PostgreSQL developers to implement compression in libpq ? That
way not only geometry would profit, but also attribute data, which can
also get quite large (in case of text). That way also slower mobile
connections (phones, tablets, notebooks) could benefit from data
compression in the future.
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.
ok - thanks for the idea.
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).
do you mean synchronizing Postgis with Postgis or Postgis with SpatiaLite?
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.
yes - that's what I was looking for. Scale, and in the future maybe also
time or potentially other variables specific to a certain map
extent/view could be defined. The select statement would have to
"digest" those variables and use them for something meaningful.
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
thanks for this other link!
Andreas
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