Does that mean if no one opens the dashboard for 12 hours (eg, between 7:59 PM Wed and 8:01 AM Thurs) that at some point Tableau will recognize that the data is stale and refresh the cache?
What if then
- the dashboard is opened 7:00 AM
- the data source is refreshed or republished at 8:15
- and the dashboard is opened 8:30
Does the user see old data or new?
5 of 5 people found this helpful
At a high level:
Items in the cache expire regardless of whether they are viewed again during the 12 hour period or not. There is no "reset" on the cache expiration time if someone views something.
Any time a data source is re-published or modified, cache is blown away. We consider a newly refreshed extract to be a new database as well - therefore cache is expired for a data source even when it's extract refreshes.
Tableau Server never proactively refreshes the cache. You have to do something to cause "an answer" to get cached - that might be an interactive viz request, it might be a subscription executing, but something is happening to make Tableau do something - Tableau doesn't care about proactively refreshing the cache itself (which makes sense - why do tons of extra work when there's no real guarantee anyone would even USE the updated cache entries...)
When something is added to the cache, a timestamp is also included in the metadata associated with the cache entry. If your viz executes 12+ hours later, it is likely vizqlserver may actually SEE the "old" cached object, however it will be ignored because it is stale. At that point, vizqlserver will execute a query, get "new" data, and that new data will be cached, essentially replacing the old stuff that wasn't good anyway.