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server.views.populate_image uses a cached image, with no way to clear the cache #568
Description
I have a series of dashboards with a live SQL connection. The workflow for these dashboards is to run a nightly refresh of the underlying data table, take a screenshot of the dashboard, and email it out to users.
The issue is that after refreshing the SQL connection, server.views.populate_image returns an image of the dashboard from before it is refreshed. (e.g., if I have data for 1/1/2020, truncate that table overnight, insert data for 1/2/2020, then use views.populate_image, it will still show 1/1/2020 data, even though that data is truncated from the underlying data table as Tableau is caching the image of the dashboard).
Here is a snippet of the offending code:
import logging
import tableauserverclient as TSC
workbook_name = "name of workbook containing view"
view_name = "view to print"
report_filter = "dashboard filter value"
filter_name = "dashboard filter name"
report_export_file_name = "file path + file name of image to be generated"
tableau_auth = [censored]
with server.auth.sign_in_with_personal_access_token(tableau_auth):
all_workbooks = TSC.Pager(server.workbooks.get)
workbook = [
wb
for wb in all_workbooks
if wb.name == workbook_name and wb.project_name == workbook_project
][0]
logging.info(f"Found workbook: {workbook_name}")
# request views from workbook and find first matching view
server.workbooks.populate_views(workbook)
view = [v for v in workbook.views if v.name == view_name][0]
logging.info(f"Downloaded view to memory: {view_name}")
# request image of view and download it locally
# maxage = max age of image cached in minutes
# shortest interval that you can use is one minute
image_req_option = TSC.ImageRequestOptions(maxage=1)
if report_filter:
image_req_option.vf(filter_name, report_filter)
server.views.populate_image(view, image_req_option)
# save file
with open(report_export_file_name, "wb") as view_png:
view_png.write(view.image)
logging.info(f"Saved view to {report_export_file_name}")
What I've tried:
Setting maxage to 1 minute, doesn't seem to work as intended, as even running this script >1 minutes after the SQL update sometimes shows a cached view.
Using workbooks.refresh method. Doesn't work as this seems to be expecting a data extract, not live SQL connection.
Activity
divinorum-webb commentedon Mar 8, 2020
Here's a way you can toss out the cache and force a fresh PNG / PDF download:
So if you run your code the first time, maybe your cache_buster=1. If you download the image again 30 minutes later, you may receive a cached version of what you just pulled.
But, if you make cache_buster=2, then you will trick Tableau into thinking it is passing in a new filter value and it voids the cache on your visual.
That parameter doesn't really do anything in your workbook -- it's simply there to invalidate the unwanted cache on your visual.
maxwqx commentedon Apr 14, 2020
@divinorum-webb I am new to the TSC. Can you give a sample code about how to add the parameter of "cache_buster".
efarmun commentedon Jul 27, 2021
@divinorum-webb nice workaround advice but can you advise the way to update parameter on server side using tsc (python) ?
Thanks.
https://community.tableau.com/s/question/0D54T00000C6AwkSAF/is-there-a-way-to-edit-a-parameter-and-its-values-within-tableau-server
jacalata commentedon Nov 10, 2021
For this workaround, you would have to add the update parameter while editing the workbook normally - either in Desktop or Web Authoring. It can't be edited through tsc.