>I'm talking about the type of index for the primary key on the database. If you make the integer primary key a clustered index, it will save you disk space and I/O for any handling the indexes. It would also avoid records being moved from one page to another as records are added.

Primary key on all tables are clustered.

>I thought you mentioned it currently contains 4 million records. So a 4 byte integer field will be fine are long as you are not reaching 2 billion records.

Yes, but that is only one table. Our transactional tables and the audit trail tables really like to have millions of new records per day.