SSAS Realtime Processing
You need to look into proactive caching for your partitions and dimensions where you can set up notifications based on a tracking table.

From the documentation:


  Proactive caching provides automatic MOLAP cache creation and
  management for OLAP objects. The cubes immediately incorporate changes
  that are made to the data in the database, based upon notifications
  received from the database. The goal of proactive caching is to
  provide the performance of traditional MOLAP, while retaining the
  immediacy and ease of management offered by ROLAP.


The subject is a bit broad for an answer and there are quite a few options and drawbacks to consider. 

In general you check the box "enable proactive caching" and pick some latency options:



and then you specify a tracking table on the "notification" tab:



What all the options such as enable ROLAP aggregations and the latency settings do is explained in more detail in this blog post or this one