If you need to access the underlying data in an SSAS measure group in Real Time with no latency (without any processing involved), proactive caching setting Real Time ROLAP has to be configured. If you work on a typical Datawarehouse, this need is not normal. But if you use SSAS for real time calculations this setup will be useful.
1) Select the Storage Settings of the partition to be configured and select Real Time ROLAP.
2) Click on Options to launch the Storage Options window as below .
Note that the Latency is mentioned as 0 (zero).
3) Go to the Notifications tab and select SQL Server (if the fact table resides in SQL Server)
You can select more than one tracking tables to watch for any updates. When the measure group is deployed SSAS watches for trace events raised against the specific tables. To do this, SSAS needs ALTER TRACE privileges in the underlying database (as mentioned in the bottom of the dialog box below)