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

[Nyall Dawson]

On Sun, 26 May 2019 at 01:48, Régis Haubourg <regis.haubourg at gmail.com> wrote:
>
> 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!

I think this could be potentially further optimised (e.g. with a
"LIMIT 1"), but I'd see how this goes on the troublesome setup
first... no point over-optimising if your query fixes the issue.

Nyall

>
> 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