Purging provides a mechanism to clear unwanted queues and queued events of a disconnected subscriber. These events take up disk space which can be utilized otherwise.
An example of when purging can be applied.
Two subscribers EventAnalytics and EC are subscribed to a publisher called M3. EC has registered to EventHub but is unavailable for a long time. Because EC is still registered, events are persisted by EventHub and keep queuing up on the disk. When EC returns, the queued up data is unwanted. Therefore, the user may want to clean up this data. A purge operation can be used in this scenario.
This kind of situation can arise in a test environment where test subscribers are registered and do not return or are intermittently available. If you are sure the subscriber never returns there is an option to delete the subscriber.
These variances of purging are supported in EventHub:
The default behavior is no purging.