Pruning efficiency in Snowflake refers to how effectively the query optimizer eliminates unnecessary micro-partitions from scanning, which directly impacts query performance. The PARTITIONS_SCANNED metric shows how many micro-partitions were actually accessed during query execution, while PARTITIONS_TOTAL represents the total number of micro-partitions in the scanned tables. The ratio of PARTITIONS_SCANNED to PARTITIONS_TOTAL indicates pruning effectiveness - a lower ratio means better pruning. The community discussion confirms this with 100% consensus on BE, explaining that 'pruning efficiency = partitions_scanned / partitions_total ratio'. Other options like EXECUTION_TIME, COMPILATION_TIME, and TOTAL_ELAPSED_TIME measure query performance timing but don't directly assess pruning efficiency.