http://www.perlmonks.org?node_id=404134


in reply to Re: Hash lookups, Database lookups, and Scalability
in thread Hash lookups, Database lookups, and Scalability

Also, if the table has a clustered index (Sybase/SQL Server) or the table is index organized (Oracle) or somesuch, there is no extra disk IO to read the row data.

(From your description with 2 physical reads, it sounds like you used a clustered PK index.)