There are other situations not covered here, but the gist of it is that the OS is very efficient at managing data access with memory mappings. Similarly, if data in RAM is unused and the OS determines that it needs to free that space for other work, then the OS will automatically "page out" that data to the disk at the other end of the memory mapping. Else the OS will "page in" the data from disk at the other end of the memory map. If the data is already there in RAM, then great, it's instantly available. CAS then references the place in memory for the data it wants. Here's an over-simplified explanation: CAS initially places the data either in RAM or on disk and then creates the memory map. The OS, not CAS, moves data to/from the backing store If the original source data is already unencrypted SASHDAT which is accessible via local storage, then CAS will memory-map to that location as the backing store instead - but just for the source data.Īll changes to in-memory data are memory mapped exclusively to the CAS_DISK_CACHE. But, CAS_DISK_CACHE is not the only backing store for in-memory data. Most of the time, CAS will memory-map any data loaded into memory to the CAS_DISK_CACHE. Memory mapping associates an address in RAM with a location in locally-accessible storage (hard disk, file system, etc.). All in-memory data is memory mapped to a locally-accessible backing store The SASHDAT structure is optimized for distributed analytic processing. However, the data that CAS has in-memory is exclusively in SASHDAT format, regardless of its original source or ultimate destination. Refer to the SAS documentation about Working with SAS Data Connectors for a lot more explanation. And of course, CAS can write that data back out into a myriad of other formats as well. CAS analyzes data in SASHDAT format, regardless of the original sourceĭata loaded into CAS can come from a variety of sources and formats thanks to the SAS Data Connector technology. This post will provide a brief but illustrative guide to the inner workings of how data is managed in memory by CAS. However, most of that behavior can be distilled down to a few simple rules which adequately describe the majority of situations. There are many twists and turns to cover all of the nuances and possibilities. To view the physical lantern slide, please contact the Architecture Library.The way that the SAS Viya Cloud Analytic Services (CAS) Server manages data in memory is a complicated topic.
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