[Qgis-user] Adding PostGIS Layer (Query Before Load)

[Jürgen E. Fischer]

Hi Peter,

On Tue, 06. Aug 2019 at 11:43:44 +0000, Peter Borissow wrote:
>  OK, after enabling  "Use estimated metadata" on the connection, the Data Source Manager comes up (doesn't hang). I am able to select a table and apply a filter. After a brief delay, QGIS starts to load data. However, is see an odd query consuming resources in the database:
> SELECT st_extent("coordinate") FROM "public"."device_location"

That should be:

SELECT st_estimatedextent("public", "device_location", "coordinate")

Ignoring the where clause is one of the tradeoffs that is used with "estimated
metadata" - also the feature count can be inaccurate (see tip on
https://docs.qgis.org/testing/en/docs/user_manual/managing_data_source/opening_data.html).

Unless that column doesn't have pg_stats (ie. SELECT count(*) FROM pg_stats
WHERE schemaname='public' AND tablename='device_location' AND
attname='coordinate' is not 1) in which case st_extent is used, but with the
where clause.


Jürgen

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