Hi @yagrus2 ,
Thanks for posting here. Firstly, please be sure to notice the difference between reading partition data multiple times and load partition data multiple times.
Load partition data multiple times could be a sign that you have memory pressure in your SSAS server, thus the partition data need to be pushed out to load the newly requested data.
While reading partition data multiple times means SSAS Formula Engine and Storage Engine need to request the data multiple times from memory cache with disk IO.
Regarding why partition, Partitioning can improve both processing performance and query performance significantly. Analysis Services can process multiple partitions in parallel and this can lead to much more efficient use of CPU and memory resources on your server while processing is taking place. Analysis Services can also fetch and aggregate data from multiple partitions in parallel when a query is run too, and again this can lead to more efficient use of CPU and memory and result in faster query performance. Lastly, Analysis Services will only scan the partitions that contain data necessary for a query and since this reduces the overall amount of IO needed this can also make queries faster.
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