What are checkpoint files?
They are data and delta files as documented in Durability for Memory-Optimized Tables. When you use disk based tables, the data is written to data files. Even though data is stored in memory for memory optimized tables, SQL Server still needs to persists data for disaster recovery. Data for memory optimized tables is stored in what we call checkpoint files. Data file contains rows from insert and update operations. Delta file contains deleted rows. Over time, these files can be ‘merged’ increase efficiency. Unneeded files after the merge can be removed eventually (but this can only happen after a log backup).
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