pn.cache only caches for a session.

[MarcSkovMadsen]

panel==1.1.0

When working on the Streamlit Migration guide in #5027 I discovered that @pn.cache only caches for a user session. Not globally.

Globally was what I and @philippjfr expected. Globally is what I need most often.

Reproduce

from time import sleep

import numpy as np
import panel as pn
from matplotlib.figure import Figure


def get_data():
    print("running get_data func")
    sleep(0.1)
    return np.random.normal(1, 1, size=100)

def plot(data, bins):
    print("running plot func", bins)
    sleep(2)
    fig = Figure(figsize=(8,4))
    ax = fig.subplots()
    ax.hist(data, bins=bins)
    return fig

pn.extension(sizing_mode="stretch_width", template="bootstrap")

data = get_data()
bins = pn.widgets.IntSlider(value=20, start=10, end=30, step=1)
cplot = pn.cache(plot)
bplot = pn.bind(cplot, data, bins)
pn.Column(bins, pn.panel(bplot, loading_indicator=True)).servable()

You can see how it reruns the plot function after a reload of the browser below.

2023-06-14_05-47-41.mp4

Additional Context

You actually need to be able to both cache things for a users session and globally. Globally probably accounts for 99% of use cases though.

You could handle this by providing two caches:

• pn.cache_user: caches for a user session
• pn.cache_global: caches globally across user session.

If we just want the one we could describe in the documentation how to get the session id (I don't know how) and use this to cache for a user session. This documentation could be added to the cache documentation https://panel.holoviz.org/how_to/caching/index.html.

See also #5028 (comment) and #5028 (comment)

I'm on windows. Don't think it matters.

[philippjfr]

I'm very confused by your example, the input to your cached function is a random array which is basically guaranteed to change each time. If you wrap the call to get_data in pn.cache then the random array stays the same each time and you'll cache hit on get_plot.

Closing this as there is no issue here.

[philippjfr]

I'll add an argument to pn.cache to support per-session caches.

[MarcSkovMadsen]

Looks like you are right. I overlooked this. Thanks