Skip folded deeper levels when rendering page tree

[pascalj]

This change is a performance improvement and should not affect the behavior of the CMS.

Previously the page tree was rendered in full even if pages are folded.
Consider the following tree: even if level 1 was folded, level 2 and 3
would get rendered and sent to the client.

- root
 |+ level 1
   |- level 2
     |- level 3

This change does two things:

1. load all user-folded pages for the current user in advance, reducing
   the number of queries to 1
2. skips all pages that are under a folded page

The result is:

- root
 |+ level 1

Together with 5a4c0d3 this speeds up the page tree rendering from 20
seconds to ~100ms when only 10 folded pages are shown (for Alchemy::Page.count == 4000). The number of queries per page tree is also constant now.

Feedback is welcome! 👂

[tvdeyen]

Makes sense! Thank you, Pascal.

I tried this locally with my "Seed 1000 Alchemy Pages" gist and did not saw any noticeable improvements, but this might be because of running this locally with sqlite and in dev mode.

As I did not found any regressions, 👍

Could you add a simple model spec for the newly introduced scope? Thanks

[pascalj]

Thanks for the gist! Yes, this certainly has an influence. I have no time to dig deeper into this, but it seems Postgres has certain problems with this part of the code or maybe it's my 3.5 branch (although including 5a4c0d3). I tried it with roughly 3k pages (5 levels with 5 sub pages each) and it outperforms my Postgres testsetup. However: both are faster with this patch:

spec/dummy with 10 * 100 pages, first level folded:
master: Completed 200 OK in 1383ms (Views: 1355.2ms | ActiveRecord: 19.0ms) (~350KB)
this branch: Completed 200 OK in 244ms (Views: 221.6ms | ActiveRecord: 13.5ms) (~60KB)

Also notice the difference in size. In the 3.5k pages example this goes down from 600kb to 4KB.

I added a model spec. The test for inheritance doesn't seem to be necessary any more. I copied it from the old implementation, but I'm not brave enough to remove it and added a test to verify it doesn't fail for non-AR user classes.

[tvdeyen]

Thanks for the specs and additional benchmarks.

[tvdeyen]

Danke Pascal und lieben Gruß

[creativej]

Great work! What's the timeline for the 4.1 release?
Any chance for this patch to go into 4.0?
We have a lot of pages in our cms it takes over 5s to load the page tree so getting this improvement would be amazing!