In Tableau Server version 2019.1 and later, workbooks and views use higher resolution thumbnails. When you upgrade to Tableau Server version 2019.1 or later, the Backgrounder runs the Enqueue Thumbnails Upgrade job and the Upgrade Thumbnails job, which refreshes thumbnails for any views that have not been edited or published since Tableau version 2018.2 and converts them from low resolution thumbnail images (192 x192 pixels) to high resolution thumbnail images (300 x 300 pixels), as shown in the figure below.
Note: Starting in Tableau Server version 2020.2 and later, the Upgrade Thumbnails job is turned off by default. Server Administrators can use tabcmd to run the Upgrade Thumbnails job. For more information, see upgradethumbnails.
When the Upgrade Thumbnails job refreshes the thumbnail images, the modified date of the view is changed to match the thumbnail update date. The Upgrade Thumbnails job does not change the modified date of workbooks when it updates the contained view's thumbnails.
Depending on the number of workbooks you have, the Upgrade Thumbnails job can run for a few minutes to a few hours. You may notice that CPU usage on Backgrounder nodes is higher than normal during the time that the Upgrade Thumbnails job is running. You may also notice that thumbnail images may appear in low resolution for up to a week after upgrading to Tableau Server 2019.1 or later, while the Upgrade Thumbnails job processes all of the thumbnail images used in your workbooks. We recommend that you wait for the Upgrade Thumbnails job to complete before you back up Tableau Server.
After the first run of the Upgrade Thumbnails job, it runs on a predefined weekly schedule. The Upgrade Thumbnails job runs at lowest priority and creates one task per workbook in the background_jobs table to upgrade any low resolution thumbnails. Low resolution thumbnails published to Tableau Server by Tableau Desktop version 2018.3 and earlier are automatically cleaned up each week when the Upgrade Thumbnails job runs.
You can check the status of the Upgrade Thumbnails job using the Background Tasks for Non Extracts administrative view(Link opens in a new window). The Upgrade Thumbnails job can display either the success or error status.
Upgrade Thumbnails job failed, or it completed but some thumbnails are still low-resolution.
The Upgrade Thumbnails job might show error status if your credentials are wrong. In that case, the workbook thumbnails will still appear in fuzzy, low-resolution (192 x192 pixels). Update your credentials, and the Upgrade Thumbnails job will update the workbook thumbnails the next time it runs.