13. února 2006 23:55
What is the benefit of setting the proactive cache to Real Time ROLAP. Wouldn't this be the same as ROLAP. Confused on why there is such an option.
Books online doesn't seem to answer it clearly.
14. února 2006 2:57Moderátor
Proactive caching adds the ability to automatically detect changes in source data and update Analysis Services objects appropriately. In the case of Real-Time ROLAP (which was also an option in AS 2000), the AS server can detect data changes (via events, polling or client-initiated notification) and invalidate its in-memory cache - without proactive caching, explicit processing would be needed to drop the cache.
Real Time ROLAP
OLAP is in real time. Detail data and aggregations are stored in relational format. The server listens for notifications when data changes and all queries reflect the current state of the data (zero latency).
This setting would typically be used for a data source with very frequent and continuous updates when the very latest data is always required by users.
14. února 2006 23:02
Thanks. I'm getting closer to understanding.
How can the latency be zero? If in the Real Time ROLAP case, reprocessing of the cube is required to modify aggregations (assuming non 0% aggregation). This would imply not zero latency, but the latency it takes to reprocess the cube. To me it seems like Real Time MOLAP is more likely to have the latest data over Real Time ROLAP. What am I missing?
15. února 2006 4:50Moderátor
I don't believe that there is a standard setting such as Real Time MOLAP - with pure MOLAP, there will be some latency while the cache is rebuilt. However, proactive caching policy can cause queries to be directed to the fact table (ROLAP mode) while the MOLAP cache is being rebuilt - but this would no longer be pure MOLAP.
According to BOL below, no aggregations are stored for Real Time OLAP, so there is probably no significant reprocessing time involved when data is updated - [MS] folks could provide more detailed info:
Partition Storage (SSAS)
Real-time ROLAP is typically used when clients want to see changes immediately. No aggregations are stored with real-time ROLAP.
29. dubna 2006 0:31
Could you please send me some code sample and "how to " for send client notification to Analysis Server?