What does 'Percentage scanned from cache' indicate in Snowflake's query profiler?

• A. The percentage of data scanned from the metadata cache.
• B. The percentage of data scanned from the query cache.
• C. The percentage of data scanned from the local disk cache.
• D. The percentage of data scanned from external storage.

Answer: (C)

The metric reflects how much of the data scanned for the query was served from the compute node’s own caching layer. Snowflake keeps recently read data blocks in a local disk cache on each virtual warehouse. When a query accesses data that’s already cached, those blocks are read from this fast local cache rather than from cloud storage, speeding up the operation. The percentage scanned from cache therefore shows what portion of the scan benefited from that cached data.

This is distinct from metadata caching (which speeds up metadata lookups and planning), the query/result cache (which can bypass execution entirely if an exact result is already stored), or the underlying external storage itself (the source of data). So a higher percentage scanned from cache means more data was read from the warehouse’s local disk cache, not from storage.