I am setting up Sitecore xDB and am trying to test exactly what info gets through the system for authenticated and non-authenticated users. I would like to be able to make a change and see the results quickly in Sitecore. I found the setting to lower session lifetime to 1 minute rather than 20. I have not found a way to just force Sitecore to sync with Mongo on demand or at least within 1-5 minutes rather than, what also appears to be about 20 minutes at the moment. Does it exist or is "rebuilding" the database explained here the only existing process?
See this blog post by Martina Welander for this and more good info about xDB sessions: https://mhwelander.net/2016/08/24/whats-in-a-session-what-exactly-happens-during-a-session-and-how-does-the-xdb-know-who-you-are/
You just need a utility page that calls System.Web.HttpContext.Current.Session.Abandon(). You may also want to redirect the user to a page that doesn't exist.
Update to address comment
My understanding is that once an xDB session has expired, processing should take place quickly. In the Sitecore.Analytics.Processing.Services.config file, the BackgroundService agent is set to run on an interval of 15 seconds by default.
You may just be seeing cached reporting data. Try clearing the cache using the /sitecore/admin/cache.aspx page. You could also decrease the defaultCacheExpiration setting for the reporting cacheProvider in the Sitecore.Analytics.Reporting.config file. The default is 10 minutes.