Explanation
The Gen2 storage architecture automatically tiers your most frequently queried columnstore segments in a cache residing on NVMe based SSDs designed for Gen2 data warehouses. Greater performance is realized when your queries retrieve segments that are residing in the cache. You can monitor and troubleshoot slow query performance by determining whether your workload is optimally leveraging the Gen2 cache.
Reference:
https://docs.microsoft.com/en-us/azure/sql-data-warehouse/sql-data-warehouse-how-to-monitor-cache