• OK, so took 26 minutes with the pydata theme commented out.
• Other recent builds took 40 minutes

I'd say the pydata theme is definitely slowing things down

The point raised on gitter about optipng is a good one. Trying with no compressing of thumbnails.

• turning off compression dropped the build time to 18 minutes (pydata theme still off)

(BTW, thanks @larsoner for the skip commands!)

Pinning pydata_theme fails, and took 48 minutes to do so. Of course its possible the failure is causing the slowness, but I would guess not.

18c4fde (collapse navigation = True and no compression) took 26 minutes. So collapsing the navigation helps substantially.

From https://pydata-sphinx-theme.readthedocs.io/en/latest/user_guide/configuring.html#configure-the-navigation-depth-and-collapsing-of-the-sidebar it looks like the default depth is 4, maybe restricting to 2 would be faster enough?

html_theme_options = {
  "navigation_depth": 2
}

(or maybe this won't speed things up at all, not sure...)

Ha, well that one took over an hour. I'm nit sure I trust circle to do these tests, so I guess I'll do them on a local machine....

OK, here is the results of tests for my machine:

all sphinx 3.5.3
sphinx-gallery                 0.9.0.dev0 
serial build (no parallel)

make clean each time
make html

compress_images: ('thumbnails', 'images'),
collapse_navigation: False
pydata-sphinx-theme:            0.6.3
commit: master
result: 2010.13s  = 33.5 minutes

compress_images: ('thumbnails', 'images'),
collapse_navigation: True
pydata-sphinx-theme:            0.6.3
commit: master
result: 1639.42s  = 27.3 minutes

compress_images: Off!
collapse_navigation: True
pydata-sphinx-theme:            0.6.3
commit: master
result: 1322.72s  = 22 minutes

compress_images: True
commit: 7d77bb9670  (no theme)
result: 1232.57s = 20.54 minutes

compress_images: False
commit: 7d77bb9670  (no theme)
result: 911.00s = 15.2 minutes

So in sum the breakdown is basically:

• fastest = 15 minutes
• new theme = +7 minutes
• compress images = +5 minutes
• uncollapsed navigation = +5 minutes

Is there any reason to compress the images on CI?

We can run CI with the navigation collapsed. Those combined should get us from 33 minutes to 22 or 23 minutes. Thats still 50% slower than without the new theme, but...

Thanks @jklymak for doing all the tests!

Is there any reason to compress the images on CI?

I don't think there is a strong reason. It makes the devdocs upload larger and viewing the devdocs costs more bandwidth, but that's bearable if the built is significantly faster.

.. sure well lets see; if it adds 5 minutes to the upload time, its not worth doing ;-)

Closed by #20727