HoloViews scatter plot hover is slow when color is set

Please see recording below, you can see that both plots have same amount of data (30000 points) and settings, but one that uses regular bokeh works fast, whereas the one that is produced via holoviews is quite slow. The other thing I noticed is that if you remove color from the holoviews plot, it works as fast as pure bokeh.

ALL software version info

bokeh: 2.4.2
holoviews: 1.14.17
python: 3.9.7
ipython: 8.0.1
ipykernel: 6.7.0
ipywidgets: 7.6.5
jupyter_client: 6.1.12
jupyter_core: 4.9.1
jupyter_server: 1.4.1
jupyterlab: 3.2.1
notebook: 6.4.6
os x: 10.15.7
chrome: 97.0.4692.99

Complete, minimal, self-contained example code that reproduces the issue

import bokeh
import numpy as np
import pandas as pd
import holoviews as hv

from bokeh.plotting import figure, show
from bokeh.io import output_notebook
from bokeh.models import LinearColorMapper
from bokeh.layouts import row

hv.extension('bokeh')
output_notebook()

n = 30000
ds = pd.DataFrame({'x': np.random.rand(n), 'y': np.random.rand(n), 'z': np.random.rand(n)})

p_bk = figure(frame_height=300, frame_width=300, title='bokeh (fast)',
           tooltips=[
               ('x', '@x'), 
               ('y', '@y'), 
               ('z', '@z')])
transform = LinearColorMapper(palette='Viridis256', low=0, high=1)
p_bk.scatter('x', 'y', source=ds, color={'field': 'z', 'transform': transform})

p_hv = hv.Points(ds, ['x', 'y'], 'z') \
    .opts(tools=['hover'], color='z', cmap='Viridis', frame_width=300, frame_height=300, title='holoviews (slow)')
p_hv = hv.render(p_hv)

show(row(p_bk, p_hv))

Screenshots or screencasts of the bug in action

https://user-images.githubusercontent.com/4602302/151662499-cf21ede4-67a2-4ecc-948c-c78f1bc6cf3c.mp4

[philippjfr]

Will reopen as bokeh performs additional rendering when setting hover properties. Therefore we should just avoid setting hover properties if they are equal to the non-hover value.

[stas-sl]

Ahh, I see… Thanks for fast reply!

Actually it is slow even if you are not setting color, and set hover_color to constant:

p_bk.scatter('x', 'y', source=ds, hover_color='red')

Then, it is probably more bokeh issue rather than holoviews and it could be closed here.