About Temperature-Based Block-Level Compression
You can specify that data is automatically compressed if it is COLD (infrequently accessed) and automatically decompressed when it becomes WARM, HOT, or VERYHOT (more frequently accessed). By default, COLD data is the 20% of the data that is the least often accessed, and HOT and VERYHOT data is the 20% of the data that is the most often accessed. WARM data is anything in between.