Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.
PriVATe database link, public database link & network database link.
Network database link is created and managed by a network domain service. A network database link can be used when any user of any database in the network specifies a GLobal object name in a SQL statement or object definition.