A clustering key in Snowflake is used to co-locate similar data within the same micro-partitions to improve query performance, especially for large tables where data is not naturally ordered or has become fragmented due to extensive DML operations. The appropriate use of a clustering key can lead to improved scan efficiency and better column compression, resulting in faster query execution times.
The indicators that it may be appropriate to use a clustering key for a table include:
* D. Queries on the table are running slower than expected: This can happen when the data in the table is not well-clustered, leading to inefficient scans during query execution.
* E. The clustering depth for the table is large: A large clustering depth indicates that the table's data is spread across many micro-partitions, which can degrade query performance as more data needs to be scanned.
References:
* Snowflake Documentation on Clustering Keys & Clustered Tables
* Snowflake Documentation on SYSTEM$CLUSTERING_INFORMATION
* Stack Overflow discussion on cluster key selection in Snowflake

Directory tables in Snowflake are used to store metadata about data files in a stage. They are not separate database objects but are conceptually similar to external tables. Directory tables do not have grantable privileges of their own

https://docs.snowflake.com/en/user-guide/snowcd.html#:~:text=SnowCD%20(i.e.%20Snowflake%20Connectivity%20Diagnostic,their%20network%20connection%20to%20Snowflake.

https://docs.snowflake.com/en/user-guide/ecosystem-analytics.html