[QGIS-Developer] qgis_editor_widget_styles table, what is it ? How to create it?

[Régis Haubourg]

Hi, Thanks Nyall for the hints.

I'm considering switching to this query instead.
SELECT * FROM pg_class WHERE relname='qgis_editor_widget_styles'

In my setup it access only to one table and uses internal indexes, when the
information_schema.tables is a view that involve a materialized query here
when using explain.
I don't see a significant difference on my local setup, I'll test it on our
customer setup before starting my (first) PR!

Cheers
Régis

Le sam. 25 mai 2019 à 05:33, Nyall Dawson <nyall.dawson at gmail.com> a écrit :

> On Fri, 24 May 2019 at 18:25, Régis Haubourg <regis.haubourg at gmail.com>
> wrote:
> >
> > Hi all,
> > I'm facing very slow opening of project files for a customer here in
> QGIS 3.4.5. Something like 7 minutes, against 30 s in QGIS 2.18.
> >
> > We are still investigating to narrow it down, but I faced a first query
> in the logs that I fail to understand.
> >
> > QGIS emits this at a point:
>
> >
> > And this query is long in our context, 1.7s, because of a very high
> number of tables and schemas in that production DB.
> >
> > I found at [0] in the postgres provider where it comes from, I found the
> associated PR [1], but I fail to understand in what workflow this table is
> created using QGIS, and what it is used for.
> >
> > Can someone put some light here ?
>
> There's a unit test at
>
>
> https://github.com/qgis/QGIS/pull/3439/files#diff-99b101819133a316786604243f3abf6eR318
>
> and
>
>
> https://github.com/qgis/QGIS/pull/3439/files#diff-03e6d7f6f76fb4bcab508984d0fd05f6R443
>
> which partially explains this -- it looks like it's a way to specify a
> default editor widget configuration for a table, which is used
> whenever that table is loaded into QGIS.
>
> >
> > select count(*)
> >
> > from information_schema.tables
> >
> > where table_name = 'qgis_editor_widget_styles' ;
> >
>
> Looks like that query could be substantially improved -- it's only
> testing for existence of the table, so calculating the count is
> inefficient and requiring a whole table scan.
>
> Nyall
>
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