The Cloud Services layer in Snowflake is responsible for various services, including security (like authentication and authorization) and metadata management (like query parsing and optimization).References:Based on general cloud architecture knowledge as of 2021.

In Snowflake,SAMPLE (5 ROWS)ensures an exact count of 5 rows is returned from MY_TABLE, regardless of table size. This is different from SAMPLE SYSTEM or SAMPLE BERNOULLI, which use percentage- based sampling, potentially returning varying row counts based on probabilistic methods.
The ROWS option is deterministic and does not depend on percentage, making it ideal when an exact row count is required.

A clustering key can be defined when a table is created by appending a CLUSTER Where each clustering key consists of one or more table columns/expressions, which can be of any data type, except GEOGRAPHY, VARIANT, OBJECT, or ARRAY https://docs.snowflake.com/en/user-guide/tables-clustering-keys

Efficient pruning in Snowflake is indicated by the number of partitions scanned out of the total available. If a small percentage of partitions are scanned, it suggests thatthe pruning process is effectively narrowing down the data, which can lead to improved query performance