复合集群PK行为vs非集群PK +非唯一集群索引

I have a table with a few columns, the 2 important ones are appid and fileid. Together, they make up a PK for the table. A typical use case for the table will be how many files contain appid x, or which appid is the most popular. Those queries will be run very often on only subsets of files as well, instead of all files. Neither column is unique individually.I have a table with a few columns, the 2 import