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 <[email protected]> a écrit : > On Fri, 24 May 2019 at 18:25, Régis Haubourg <[email protected]> > 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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