Which statement best describes the impact of spilling to disk on performance?

• A. Spilling makes queries faster.
• B. Spilling generally increases execution time due to extra IO.
• C. Spilling has no effect on performance.
• D. Spilling reduces CPU usage.

Answer: (B)

Spilling to disk happens when a query runs out of memory and temporarily stores intermediate data on disk to free up RAM. That introduces extra IO: data must be written to disk and later read back into memory for processing. Disk access is much slower than memory access, so these additional read/write operations create latency and limit throughput, causing the overall execution time to increase. While spilling can help avoid out-of-memory errors and reduce memory pressure, the net effect is typically longer runtimes. It doesn’t make queries faster, and it doesn’t generally reduce CPU usage in a way that improves performance—the dominant impact is the slower IO-bound work introduced by spilling.