Refresh and caching
External data sources re-fetch their data on a schedule. These options live in the datasource editor's Advanced settings panel, under Refresh settings and Cache settings, and control how often a data source refreshes and how the resources it fetches are cached.
Refresh type
In the Refresh type field, choose how often the datasource checks for new data.
Simple interval
Refreshes every X seconds. Set the number in Refresh interval (seconds), for example 3600 for hourly or 86400 for daily.
Advanced schedule (cron)
Refreshes at exact times, set in Cron expression with Quartz cron syntax.
- Set a Timezone for the expression, so the schedule runs at the right local time.
| “At 04:05.” | 5 4 * * * ? |
|---|---|
| "At 22:00 on every day-of-week from Monday through Friday.” | 0 22 * * 1-5 |
| “At 14:00 on Sunday.” | 00 14 * * sun |
| “Every 5 minutes.” | 0 */5 * * * * |
| “Every hour.” | 0 0 */1 * * * |
| “Daily at 9:00 AM.” | 0 0 9 * * * |
- You can create cron expressions here
- Or create one in the Cron manager by clicking the icon next to the field
Continue refreshing despite errors
Learn more: Continue refreshing despite errors
Caching
Store external data locally
Stores external content (images, files) referenced in the data on your Wallboard server for faster access.
- Remove broken file links automatically: Broken external resource URLs are removed from the datasource.
- Clear cache when data updates: When the datasource updates, the stored resources are replaced with fresh ones.
- Recommended for content where the data source may contain a large number of elements that become obsolete over time, such as bus timetables or time-based events like our meetingroom solution
- Update internal file references: The cached external URLs are replaced with the cache location.
Some datasources always cache their resources, because your screens could not display them any other way:
- SharePoint Lists: images stored in SharePoint require a Microsoft sign-in, so the datasource downloads them with its credential. The caching settings have no effect.
- User Active Directory with Fetch profile pictures enabled: the profile photos also require a Microsoft sign-in.
- File from URL and Power BI: these datasources exist to deliver a file, so the file is always stored on your Wallboard server.
Follow external refresh recommendations
When enabled, the data source will use the expiration time from the URL’s cache-control header to calculate the next update time to ensure that the data stays up-to-date while avoiding unnecessary requests.
Cache-control expiration is greater
- If the cache-control expiration time is greater than the configured refresh interval or cron schedule, the data source refreshes based on the Cache-Control expiration
Cache-control header: 300s
Refresh interval (seconds): 60s
If Follow external refresh recommendations is enabled, the datasource will refresh every 300 seconds, as the source data updates at that interval.
Therefore, checking for updates every 60 seconds would be unnecessary
Refresh interval is greater
- If the cache-control expiration time is lesser, the data source follows the manually set refresh time
Cache-control header: 300s
Refresh interval (seconds): 600s
If Follow external refresh recommendations is enabled, the datasource will refresh every 600 seconds, since the source can update twice within that interval.
This may lead to information loss due to missed updates.