dcc.Loading Component Causes Forced reflow therefore very slow

Dash Python
1

So I have a fairly complex dashboard hiding behind a Loading component, and every time a callback is fired, it became really sluggish and Chrome profiler showing a 5 secs ‘Recalculate Style’, and this points to a culprit Forced reflow (Avoid Large, Complex Layouts and Layout Thrashing  |  Web Fundamentals) .

I’m not a front end developer but then I suspect the loading anim could cause this, because it seems reconstruct the whole DOM, so I removed the loading, and then it became much faster from 5 sec to around 1 sec, but of course there were no nice loading animation.

So I was wondering if anyone has similar experience?

  1. Is it true that dcc.Loading Component is to blame? (it certainly points this way)
  2. If so, any recommendation? I really like the loading effects it would be a shame having to drop it because of performance.

For your reference, the code is pretty standard, it’s like this:

app.layout = html.Div([
    dcc.Location(id="url", refresh=False),
    html.Div(id="page-content"),
    # dcc.Loading(children=html.Div(id="page-content"), type="graph", fullscreen=True),
])

It’s a multi page app, and I have a callback on URL that updates the page-content element. Inside the callback is the actual dashboard with its own callbacks.

Thanks.

2

Just to verify, could you report which version your on?

print(dash.__version__)

. and if you are on an older version, could you try upgrading and see if the issue remains?

pip install dash —upgrade
3

Thanks for the reply, I’m on Dash 1.12.0; dash-core-components is 1.10.0 . I could try updating the library, but even with my current versions, is it likely to cause this problem? I have some production system on the version so prefer to stay with the these ones…

4

We did change the internals behind how the loading behaviour works in 1.13.x in order to improve the performance, so it’s possible this could help your situation.

5
6

Okay so i have tried in v1.13.4, unfortunately, no obvious difference still very slow with loading component.