[QGIS-Developer] QGIS "fast" mode

Régis Haubourg regis.haubourg at gmail.com
Sat Mar 14 04:58:03 PDT 2020

Hi Tomas.
Check the project property option named "trust". This is exactly what it is
supposed to do.
I admit the wording is not nice, any better idea is welcome.
Best regards

Le sam. 14 mars 2020 à 12:55, Tomas Straupis <tomasstraupis at gmail.com> a
écrit :

> Hello
>   I would like to know opinion of QGIS developer community on the
> question of "self-fixing queries" in the context of database layers.
>   When you add a new database layer, QGIS queries required data, asks
> user for other information and then saves it in the project file.
>   Now when you re-open the project, QGIS is re-querying a lot of data
> which is already saved in the project: geometry type, srid, attributes
> (table columns/types).
>   The downsides are:
>   * these "re-checking" queries take considerable time on large
> databases: with millions of records from 1minute up to several hours,
> database is tuned - WMS/WFS queries finish in ~100ms.
>   * in QGIS server environment these re-checking queries are executed
> each time when apache launches a new QGIS server process
>   * QGIS might by itself (without human interaction) decide to  work
> differently compared to what it was asked to do when the project was
> created if it finds that "something has changed"
>   * re-checking during project opening is not 100% correct, as if
> changes are possible in principle, then data/schema could change
> during the time QGIS (Desktop/Server) is open/running
>   * in environments other than development (testing, qa, production),
> database schema should never change without some clear procedure which
> should also include updating QGIS project files and testing them as
> required, therefore such re-checkings should never be required on
> testing/production environments.
>   I do understand that the current situation/understanding is
> different from mine, so in order to satisfy everybody, maybe it would
> be feasible to add say an environment variable like QGIS_FAST=TRUE (or
> QGIS_PRODUCTION=TRUE) and if this is set - re-checking queries could
> be skipped? We've been running modified QGIS without re-checking in
> production for months and are very happy with results. This should
> also improve the benchmarks of QGIS Server as it is known that initial
> opening of the project takes considerable amount of time.
>   What is your opinion?
>   Thank you
> --
> Tomas
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